Green Approach to Dye Wastewater Treatment Using Biocoagulants

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Green approach to Dye Wastewater Treatment using Biocoagulants Chethana Mudenur, Laxmi Gayatri Sorokhaibam, Vinay Bhandari, S. Raja, and Vivek V. Ranade ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.5b01553 • Publication Date (Web): 23 Mar 2016 Downloaded from http://pubs.acs.org on March 23, 2016

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ACS Sustainable Chemistry & Engineering

Green approach Biocoagulants

to

Dye

Wastewater

Treatment

using

Chethana M.§, Laxmi Gayatri Sorokhaibam*‡, Vinay M. Bhandari∗§, S. Raja† and Vivek V. Ranade§

§

Chemical Engineering and Process Development Division, CSIR-National Chemical Laboratory, Pune – 411008, India † Manipal Institute of Technology, Manipal – 576104, India

ABSTRACT

The present study focuses on newer bio-coagulants, bio-formulations and understanding of coagulant behaviour with biocoagulants vis a vis chemical coagulants. Newer biocoagulants- seeds of Azadirachta indica (AI) and pads of Acanthocereus tetragonus have been discussed along with two known bio-coagulants- Moringa oleifera and Cicer arietinum seeds. Dye removal studies have been carried out using widely reported Congo red dye to facilitate easy comparison with other conventional coagulants and the effect of various parameters such as initial dye concentration, pH, coagulant dose etc. have been discussed in detail. The use of bio-coagulant was found to be highly effective and up to 99% dye removal could be achieved for coagulant doses in the range 300-1500 mg/L. It was also observed that coagulation is pH sensitive, similar to chemical coagulants. Though the biocoagulant dose is relatively higher than conventional chemical coagulants, a good value of sludge volume index - ~50 mL/g for 1 h and 30 min was obtained for two coagulantsAcanthocereus tetragonus and Moringa oleifera. A very high particle count compared to

∗

Corresponding author. Tel: +91-2590-2171;Fax: +91 2025893041. E-mail: [email protected] (V.M. Bhandari) [email protected] (Laxmi Gayatri Sorokhaibam)

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chemical coagulants was seen using focused beam reflectance measurement.

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Bio-

formulation with chemical coagulants such as alum, ferric and aluminium based coagulants can not only lower doses of biocoagulants (up to one third) but can also result in significant improvement in the coagulation performance-up to 50% or more. KEY WORDS: Effluent treatment, Coagulation, Flocculation, Dye removal, Pollution.

INTRODUCTION Industrial wastewater treatment of dye wastewaters is a challenging problem, especially when the refractory pollutants are present that are difficult to degrade using conventional biological treatment methods which are often reported to have inconsistency in quality and quantity of treatment1. Further, some of the dyes can cause serious damage to the environment- aquatic system and surrounding land.2 Although, the discussion on the hazardous nature of these dyes is beyond the scope of this paper, it is important to note that despite the carcinogenic and mutagenic effects, over 50,000 tons of dyes are discharged into the environment annually.3 The wastewater stream, many a times, also contains metal pollutants such as copper, iron, chromium, which has a cumulative effect, and higher possibilities for entering into the food chain. The complex nature of wastewater is evident from the fact that it has deep colour, high concentrations of organics, high COD, can have high ammoniacal nitrogen content ranging from few mg/L to 1000 mg/L or even more apart from the presence of other inorganics/ metals. In view of the fact that many dyes/textile and allied industries that produce or use these dyes generate huge volumes of wastewaters and limitations to the existing effluent treatment processes (either process or cost), it is imperative that newer methodologies be researched and applied suitably. Methods that align closely to nature be preferred in this regard since they can help in maintaining ecological balance through the use of localized green resources for the treatment. Thus, current practices require 2 ACS Paragon Plus Environment

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more techno-economically feasible biological options, lesser generation of secondary waste and improved methodologies to meet stringent pollution control norms worldwide.4,5 A large number of treatment methodologies are available commercially that employ either removal or destructive techniques depending upon the composition of the effluent. The common removal methods include coagulation, adsorption, membrane separations, while destructive methods include biological treatments, advanced oxidation processes, cavitation, incineration etc. 4,6 In view of the complex nature of the effluent, treatment strategy requires a careful selection from various physicochemical methods and biological methods of treatment for recovery of material(s), energy and destruction/disposal. In effluent treatment, coagulation process is invariably used along with other physico-chemical or biological treatment methods. Coagulation, in general, refers to a physico-chemical process through charge neutralization of charged colloidal pollutant particles followed by removal of pollutants through settling of aggregates formed. Chemical coagulation process is commonly employed in this regard while electro-coagulation is an emerging alternative. Biocoagulation, though known, has not been employed widely so far. The coagulants can be inorganic or organic coagulants such as aluminium, iron, and magnesium salts; lime, hydroxyethyl cellulose, polyvinyl alcohol, polyacrylamides, proteins, polysaccharides etc.. Coagulation is simple to operate, can handle high initial concentrations and is comparatively less expensive. However, coagulation process is invariably associated with the generation of secondary waste stream in the form of sludge and low sludge volume is crucial to the process. The use of chemical coagulants having specific properties such as inorganic or organic polymers can, however, be expensive as compared to common coagulants. A trade-off is required in terms of coagulant dose, process efficiency, cost of coagulants /operation and sludge disposal problems. Thus, it is instructive to explore and develop alternative coagulants that are environmentally friendly, inexpensive and practically suitable for wastewater treatment. 3 ACS Paragon Plus Environment


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A number of plant-based natural coagulants have been studied in the past and prominent bio-coagulants include Moringa oleifera, Stryconus potatorum, Cactus species, Phaseolus vulgaris, surjana seed, maize seed, tannin, gum arabic, Prosopis juliﬂora and Ipomoea dasysperma seed gum. Among these, Cactaceae family shows outstanding ability to adapt to adverse and contrasting environments ranging from drought to high and low temperatures, and can also survive in soils poor in nutrients and organic matter. 7,8 It has been recognized for its medicinal properties, dietary food sources and the pulp material are usually composed of several carbohydrates and proteins. Cactaceae is reported to exhibit the ability to transform various toxic textile dyes, including Reactive Red 141 into less phytotoxic, nonhazardous metabolites.9

The plant-based coagulants are easy to use as it requires less

processing and can provide a sustainable means for treatment.

10,11

In spite of the known

properties of many of the bio-coagulants, only a few have been studied in detail for practical applications. Moringa oleifera was reported for dye wastewater treatment while Cicer arietinum was found to be an effective coagulant for reduction of turbidity 12. Acanthocereus tetragonus (common names include Night-blooming Cereus, Barbed-wire Cactus, Sword Pear, Dildo Cactus, Triangle Cactus) for dye wastewater treatment was reported recently.13 It is one of the 660 species of Cactaceae family, has tall, columnar and dark green cactus which is also cultivated as an ornamental plant. The practical utility of this species is evident from the fact that flowers and tender shoots are edible and have medicinal properties; peel and pulp extracts of fruits have high antimicrobial activity. Although Opuntia spp. have been widely studied for its coagulating potential14, Acanthocereus tetragonas was reported as coagulants only recently for dye wastewater treatment. Further, most of the bio-coagulants were reported with purified forms after the extraction of proteins and use of natural resources as such or with minimum modifications was less common.


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In view of the limited information on bio-coagulants, especially for dye wastewater treatment, it is worthwhile to explore the potential of different biocoagulants without using purification/extraction steps. A new biocoagulant- Azadirachta indica has also been reported for dye wastewater treatment for the first time. An attempt has also been made to improve the process performance by way of developing formulations using combinations of different chemical coagulants and bio-coagulants. The performance of coagulation depends on the aggregation of the particles for which size and number of particles are most critical. Since, in-line measurement of aggregation/ flocculation, particle size distribution is difficult, focused beam reflectance measurement (FBRM), traditionally been used to study crystallization processes, was employed to study flocculation kinetics. The FBRM technique involves a solid-state laser light source providing a continuous beam of monochromatic light that is launched down FBRM probe through a sapphire window. An intricate set of lenses focuses the laser light to a small spot. This focal spot was carefully calibrated to be positioned at the interface between the probe window and the actual process. A precision motor - pneumatic or electric - was used to rotate the precision optics at a constant speed. The focused beam scans a circular path at the interface between the probe window and the particle system. As the scanning focused beam sweeps across the face of the probe window, individual particles or particle structures will backscatter the laser light back to the probe. Particles and droplets closest to the probe window get located in the scanning focused spot and backscatter distinct pulses of reflected light. These pulses of backscattered light were detected by the probe and translated into Chord Lengths based on the simple calculation of the scan speed (velocity) multiplied by the pulse width (time) or the time lag between laser emission and reflection15; a chord length is simply defined as the straight-line distance from one edge of a particle or particle structure to another edge. Thousands of individual chord lengths get typically measured each second to produce the 5 ACS Paragon Plus Environment


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Chord Length Distribution which is the fundamental measurement provided by FBRM. The Chord Length Distribution, as a “fingerprint” of the particle system, provides the ability to detect and monitor changes in particle dimension and particle count in real time. Unlike other particle size analysis techniques, FBRM measurements have no assumption of particle shape. FBRM device has been successfully used for real-time monitoring of the chord length distribution of the particles in the suspension. However, FBRM can also be used to monitor particle concentrations, dimensions, and size distributions in-line, even in high-consistency suspensions.16 In the present study, FBRM was used to predict the changes in the particle size with respect to time for three stages (mixing, flocculation, sedimentation) of the coagulation process. EXPERIMENTAL SECTION Materials The plant pads of natural coagulant Acanthocereus tetragonus and Azadirachta indica fruits were collected from National Chemical Laboratory (NCL) Pune campus, Cicer arietinum and Moringa oleifera were purchased from local markets. Chemical coagulants; Aluminum sulphate hexadecahydrate, Iron (III) chloride hexahydrate, PAC (medium), PAC SAB18, Iron (II) sulphate heptahydrate obtained from Sigma-Aldrich and Congo red indicator dye used in this study was procured from Loba Chemie. All chemicals/ reagents used in the study were of analytical grade. Preparation and extraction of biocoagulant Preparation of Azadirachta indica coagulant: Azadirachta indica fruits were collected and washed thoroughly with tap water; pulp and seeds were separated, chopped into small


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pieces, ground and extracted with water (equal weight by volume ratio). The final mass was filtered to get active coagulant material as indicated in Figure 1(a). Preparation of Acanthocereus tetragonus coagulant: Acanthocereus tetragonus pods were collected and after washing thoroughly with tap water and removing the spines, were chopped into small pieces. The external skins, as well as the inner off-white portion of the cactus pieces, were used for grinding and extraction was carried out using water in equal weight by volume ratio. The fibrous part of the pads was removed by filtration and the active ingredient of the coagulant was collected in the form of residual water extract shown in Figure 1(b). Fresh extracts were prepared for each run. The pads can be stored under refrigeration for at least 1 month without loss in activity. Preparation of Moringa oleifera coagulant: Moringa oleifera seeds were deshelled, dried at ambient temperatures for one day before milling. The whole kernels were milled into fine powder, sieved through small mesh to get fine powder and were collected in well capped sterile bottles. It can be stored under refrigeration conditions at for 3-4 0C. Figure 1(c) shows preparation of Moringa oleifera seed solution by dissolving 5 g of powder with 100 ml of distilled water, stirring for 30 minutes to extract the active coagulant material from the seed powder and the extracted solution to be used for the treatment of the synthetic dye waste water. Preparation of Cicer arietinum coagulant: Cicer arietinum seeds were ground to powder (Figure 1(d)), sieved and powder was used as a coagulant. It can also be stored under refrigeration for at least one month.



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Figure 1. (a). Extracting juice (coagulant) from Azadirachta indica (b) Extraction of cactus juice (coagulant) from Acanthocereus tetragonus (c) Process of extracting the active coagulant from the seeds of Moringa oleifera (d) Cicer arietinum powder from seeds Evaluation of biocoagulants and coagulation studies Coagulation studies were carried out using a synthetic dye wastewater solution of known concentration. Congo Red dye was chosen specifically to facilitate easy comparison of the results of this work with those reported on this dye using other chemical coagulants.


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A stock solution was prepared by dissolving dye in a concentration of 500 ppm. Further dilutions were made to make exact required concentrations using this stock solution (e.g. 50 and 100 ppm). The coagulation behaviour was studied using a standard jar test apparatus (Stuart SW6, UK) which consisted of six paddles with six beakers. Dye solutions of predetermined concentrations were taken in these beakers and predetermined coagulant dose was added; subsequently, rapid mixing at 200 rpm for 5 min followed by slow mixing at 50 rpm for 15min. The settling time of 1h and 30 min was provided for Acanthocereus tetragonus and Moringa oleifera respectively. Dye removal corresponding to various doses of bio-coagulants was measured to determine the optimum bio-coagulant dose and for minimum sludge. Typically, 900 mg/L of Acanthocereus tetragonus extract for (50,100 500 ppm dye) and ̴ 1500 mg/L (50 ppm of dye), ̴ 3800 mg/L (100, 500 ppm of dye) of Moringa oleifera can be considered as the optimum dose. Effect of pH was studied using this optimum dosage. Analysis of the samples was made using 50 ml of the supernatant liquid. Dye concentration was analyzed using spectrophotometer spectroquant pharo-100 at λmax value of 498 nm while Spectralab multipara-5 pH meter was used for pH measurements. Reproducibility check for representative experiments have indicated error within acceptable range of less than 5% in most cases. The percentage reduction in dye concentration was calculated by using the difference between initial and final concentrations. The sludge characteristic is given by sludge volume index (SVI) which is measured as,

Sludge volumeindex (mL / g) =

Settled sludge volume (mL / L) ×1000 Suspended solids (mg / L)

(1)

A standard laboratory method where the entire suspension after coagulation/flocculation was allowed to settle for 30 mins in a 1L graduated measuring cylinder and the volume occupied by settled sludge in mL/L and mixed liquor suspended solids in mg/L was determined. The



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settled sludge was dried at (103-105) ±2 °C for 1 h and placed in a desiccator before weighing for determination of MLSS required for determination of SVI.

FTIR analysis of the bioflocculant and the sludge

The Fourier Transform Infra-red (FTIR) of the bio-coagulant extracts and sludge composites were recorded using Perkin Elmer FTIR spectrophotometer. The spectra in Transmission mode were collected from 4000 to 400 cm-1 and average over 10 scans (resolution ± 4 cm-1). The liquid samples of the extract were exposed for FTIR measurement by dripping several drops of the coagulant sample into the KBr aperture plate. The sludge composite formed by the combination of crude plant extract with the suspension after coagulation was dried at 100±2 °C for 24 h in an oven, after decanting the excess liquid content and finally crushed to powder for recording the spectra by KBr pellet method. FBRM study of Coagulation-flocculation The main objective of the FBRM study was to characterize the flocculation process, extent of aggregation taking into consideration the size of the particles formed and the settling rate. In the present study, 300 ml of the dye solution was used in 500 mL tall glass beaker placed on FBRM beaker stand equipped with turbine blades; using four chemical coagulants and two bio-coagulants at ambient temperature (~27 °C). The FBRM probe was held in vertical position near the wall of the beaker and above the turbine. The coagulants were stirred along with the dye solution at 200 rpm for 5 minutes (rapid mixing) followed by slow mixing at 50 rpm for 15 minutes and finally providing a settling time of 30 min. Coagulation/aggregation was studied in all the three stages of coagulation with allowance made for the ports to insert measurement probes. The instrument records the data in real time using iC FBRM™ software to understand the particle system dynamics and for optimizing 10 ACS Paragon Plus Environment

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the experimental design. Inline flocs measurements involve Focused Beam Reflectance Measurement (FBRM), Mettler Toledo, where the FBRM probe utilizes a highly focused laser beam, rotating at high speed scanning the particles passing through the measurement zone. When the particles intersect the beam the laser light is back scattered. The duration of the backscatter is related to the size of the particle/flocs and can be expressed in terms of the chord length. FBRM measurements were made over the size range of 0.5-1000 µm and the measurement duration was set for every 2 second interval. The results in terms of Chord length distribution (CLD) for different coagulants can be used for differentiating the process behaviour and an integration of ‘chords’ provide the total count value. RESULTS AND DISCUSSION

Effect of coagulant dose on dye removal Coagulant dose is an important parameter in coagulation/flocculation and it is necessary to evaluate optimum dose for best performance along with techno-economic viability to prevent overdosing of coagulant during wastewater treatment17. Dosages lower than the optimum may result in insufficient floc formation, while dosage higher than the optimum leads to re-stabilization of the flocs, adversely affecting dye removal.

Figure 2. Dye removal using Azadirachta indica as coagulant 11 ACS Paragon Plus Environment


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Figure 2 shows coagulation behaviour of a new coagulant Azadirachta indica and it can be seen that close to 80 % dye removal was possible using these bio-coagulant. Further, it was also observed that the dose of this new bio-coagulant was comparatively much less than the conventional bio-coagulants. However, in-spite of significant dye reduction, even at lower coagulant dose, the settling time required for this new bio-coagulant was significantly high (~ 72 h). Thus, the new bio-coagulant may need flocculant aid to make it applicable for practical use. In view of the very high settling time (~72 h) in the case of Azadirachta indica (AI), the other biocoagulants were investigated in detail, though this new coagulant has shown good potential for dye removal. Similar to Azadirachta indica, Cicer arietinum, though effective as a bio-coagulant, indicating ~95% dye removal (Figure 3), had a settling time of 72h and thus has limitations in practical applications. Normal sedimentation does not take place in the absence of coagulant. However, the longer sedimentation time for Cicer arietinum biocoagulant may be due to smaller sized flocs which took longer duration for sedimentation. A proper combination with some other flocculant aid that may help in aggregation and quick settling of the flocs may reduce the sedimentation time. Further study to improve the sedimentation time is required in this regard. Further, Cicer arietinum has not been studied in the literature for dye removal or any specific coagulation application so far and only application in turbidity removal was reported.12 Thus, both Azadirachta indica and Cicer arietinum need further detailed studies to improve the efficiency and for improving settling characteristics of these coagulants that can make these two newer biocoagulants potentially attractive.


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Figure 3. Dye removal and colour removal pattern using Cicer arietinum as a coagulant. In comparison to the above two bio-coagulants, our earlier work on Acanthocereus tetragonus bio-coagulant had indicated highly promising results. 13 The extent of dye removal was found to improve with increase in the dye concentration and removal of 97% can be found with 1200 mg/L for Congo red dye concentration of 500 ppm, though with high retention time of 20 h. However, satisfactory reduction levels of ~65% for 6 h could also be considered. In the case of Moringa oleifera, maximum reduction was found at ̴ 1500 mg/L for low concentrations of 50 ppm while substantially higher dosage >2300 mg/L was required for higher concentrations (>100 ppm). The results Figure 4 clearly show that decrease in removal ability with the increase in dye concentration, though total dye removal is possible at lower initial dye concentration. Moringa oleifera coagulants gave the shortest settling time of 30 min amongst the studied biocoagulants. Patel and Vashi

18

reported ~70% dye reduction for Congo Red (initial dye

concentration 200 ppm) using Moringa oleifera after extracting oil from the seeds, while 13 ACS Paragon Plus Environment


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Vijayaraghavan and Shanthakumar 19 and Tie et al 20 reported ~83 % and 95% dye removal for a very low concentration of dye (25-50 ppm). All the previous studies used bio-coagulants after purification and practical applicability was not satisfactorily addressed. Effect of pH on dye concentration The pH sensitivity is an important aspect in any coagulation, and specifically in inorganic coagulant usage. In this regard, the bio-coagulants were most effective in the acidic pH, more specifically at pH 3 which is rather surprising no coagulation was observed at pH 3 without coagulant); e.g. Acanthocereus tetragonus can remove 90% dye at a dose of 9001200 mg/L, even at a high dye concentration of 500 ppm, though sensitivity to pH was less when dilute concentrations were considered.

13

Moringa oleifera was found to have an

effective pH range of 3-5, and removal efficiency of close to 100% can be obtained at low dye concentrations (dose ̴ 1500 mg/L). However, removal efficiency decreases drastically as pH increases at higher concentrations (Figure 5). The pH study can be used in developing plausible mechanism for coagulationflocculation. Significant coagulant performance in acidic region shows possible involvement of non-ionic polymers, participation of few ionized groups and adsorption through H-bonding as predominant mechanism which is often found in coagulant extracts from natural sources21,17. As indicated in Table 3 too, the studied biocoagulants had good proteinaceous content and under acidic conditions, the amino groups of the protein may get protonated to provide better interaction with the anionic portion of the dye ie. sulfonic functional group of the colloidal dye suspension. Further, with increased alkalinity, the carboxyl group of protein develops negative charge (COO_) which may result in electrostatic repulsion and enhance the solubility of dyes, which correlates well with lower coagulant performance at higher pH22. It was reflected in Fig. 5 for relatively higher dye concentrations of 100 and 500 ppm. At very 14 ACS Paragon Plus Environment

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low concentration of the dye (50 pmm), keeping the coagulant dose fixed,

the same

efficiency was achieved both in the acidic and alkaline range. The role of pH at lower dye concentration was almost negligible. A further investigation to understand this phenomenon is, however, required.

Figure 4. Effect of Moringa oleifera doses on dye removal

Figure 5. Effect of pH using Moringa oleifera coagulant; Coagulant dose:1500 mg/L



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Sludge volume index using biocoagulants It is essential for any coagulation process that sludge formation be kept less to reduce secondary waste and reduce the cost of disposal. Conforming to this low sludge volume requirement, coagulation process is recommended to have a Sludge Volume Index (SVI) in the range of 50 to 80 mL/g.

23–25

SVI indicates the morphological state and settling ability of

the aggregates. A large number of small flocs/particles that do not settle will lead to the increase in turbidity of the solution. 18 The measured sludge volume index (SVI) for Moringa oleifera, shown in the Figure 6 revealed the variability of sludge with the variation in the coagulant dose. Lower the SVI, better the sludge settling. The values between 50-100 mL/g are considered as good with good stability.

26,27

SVI is one useful parameter to determine the sludge settling characteristics in

the case of wastewater treatment and typically SVI values obtained in the coagulation process lie in the range 20-160 mL/g. The results of our work indicated SVI for the optimum dose of the Moringa oleifera coagulant in the range 32- 41 mL/g compared to that of Acanthocereus tetragonus 38-48 mL/g. This clearly highlights the advantage with the biocoagulants as the volume of the sludge produced was less as compared to that using conventional chemical coagulant.

Figure 6 . Sludge volume index at different coagulant dose of Moringa oleifera 16 ACS Paragon Plus Environment

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Storage stability and Seasonal variations Storage stability of any bio-material is typically a concern as the quality usually deteriorates over a period of time. Thus, it is instructive to evaluate the stability of the biocoagulants so that its utility is more on practical applications. In the present study, stability of the bio-coagulants (extract) was investigated after 30 days of storage under refrigeration (4 °C) and the results in terms of reduction in dye concentration are given in Table 2. It is evident that Moringa oleifera shows practically the same dye reduction compared to the fresh powder while for Acanthocereus tetragonus the results appear to improve marginally after storage. Thus, it was found that the bio-coagulants can be safely used over a period of time without any significant loss in activity. Table 2 Storage stability of Biocoagulants (Fresh versus 1 month storage) on dye reduction Moringa oleifera Dose (mg/L) 800 1500 2300 3100 3800 4500 a

Dyea reduction (before storage) 70.5 99.4 99 98.5 98.5 98.5

dye reduction (after storage) 70 99 98 98 98 98

Acanthocereus tetragonus dose (mg/L) 300 600 900 1200 1500 1800

dye reduction (before storage) 35 70 82 80 76 74

dye reduction (after storage) 38 82 92 88 87 90

Initial dye concentration 50 and 100 ppm for Moringa oleifera and Acanthocereus tetragonus respectively

Seasonal variation on coagulant performance of Acanthocereus tetragonus The source of bio-coagulant materials available in nature is mostly seasonal. Thus, it is likely that performance differs on the basis of the season. In order to evaluate if such seasonal variations exist or if it exists, the extent of the same, a model bio-coagulantAcanthocereus tetragonus was tested for seasonal changes for a 50 ppm initial dye



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concentration. The results are shown in Figure 7, which clearly indicate high sensitivity to seasonal changes. The variations are rather difficult to explain and can be partly attributed to water/moisture content of the plant material which was more in the rainy season while significantly less in summer. In order to achieve the same coagulation efficiency throughout the season, controlling of moisture content, humidity and temperature is required28 as it preserves the active ingredients present in the plant extract used as coagulant. This would impact the concentration of the active coagulant biomass in the plant that affects its performance. Further, drastic increase in the time for obtaining an effective reduction was observed, e.g. 30 min in summer to 20 h in the rainy season for a 80% reduction in the dye. A proper method of preservation, such as freeze-drying may help in overcoming the variations in coagulation activity.

Figure 7. Seasonal variation in coagulant behaviour of Acanthocereus tetragonus


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Development of Biocoagulant formulation Formulation is a blend of two or more substances (physical or reacted form) in a particular ratio to make a concoction for increased activity or performance improvement. Thus, formulations are expected to have higher activity compared to constituent individual components for a particular action or application in a synergistic manner and the action may be simultaneous, discrete or sequential. In the field of coagulants, the driving force for the development of formulations is to combine the advantages of both inorganic and organic coagulants for increased performance/ process efficiency along with cost reduction.21,27 For bio-coagulants, however, there has been no detailed investigation for the development of formulations either using other bio-coagulants or with conventional chemical coagulants. Thus, in the present work, formulation development through physical blending of two different coagulants, one of which is biocoagulant, was explored. The compositions of the biocoagulant formulations were prepared after studying the respective coagulant efficiency of the natural coagulants. Two common chemical coagulantsFeCl3 and alum; and one polymeric inorganic coagulant, Polyaluminium chloride(PAC) were combined at different doses of 10, 20 and 30 mg/L with two natural coagulants which showed good efficiency(Moringa and Acanthocereus). Two lower doses of biocoagulant which were individually studied (800 and 1500 mg/L for Moringa; 300 and 600 mg/L for Acanthocereus) were selected to test the efficiency in the bioformulations developed.

Figure 8 (a-d) shows a comparison of coagulation behaviour with individual coagulants and using biocoagulant formulations using 100 ppm dye solution. The horizontal arrow lines in the plots represent the extent of dye removal corresponding to single 19 ACS Paragon Plus Environment


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biocoagulant for the given concentration. It is evident that a very high improvement can be obtained when Moringa oleifera was used in combination with Fe (III) chloride coagulant. The dye removal using either inorganic or bio-coagulant individually was far less as compared to that in biocoagulant formulations and near complete removal was possible using bio-coagulant formulations using significantly lower coagulant dose.

Figure 8. Improved coagulation using Bioformulations (a) Iron (III) chloride with Moringa oleifera (b) Aluminum sulfate with Moringa oleifera (c) PAC with Moringa oleifera (d) Iron (III) chloride with Acanthocereus tetragonus Similarly, bio-coagulant formulation of Aluminum sulfate with Moringa oleifera can yield complete removal for 30 mg/L, close to 50 % for 10 mg/L and 75-98 % for 20 mg/L of Aluminum sulfate(Fig. 8 b). Moringa which has only 70 % removal at 800 ppm doses,


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shows an improved coagulation with the same dose but in combination with Alum which can be seen from the portion above the horizontal dotted lines in Fig. 8 b. Since the results with common inorganic coagulant such as alum and Fe-chloride are highly encouraging, development of formulation can also be extended to inorganic polymers such as Polyaluminum chloride. The results using PAC with Moringa oleifera were also similar- 99% removal for PAC content of 30 mg/L in the formulation. Comparatively lower doses of Moringa oleifera were required here (800 mg/L) and this appears to be the best formulation for maximum reduction. Acanthocereus tetragonus behaviour was slightly different and significantly better when combined with chemical coagulants. A reduction of 92% was observed when combined with the Iron (III) chloride (10 mg/L) for lesser doses of Acanthocereus tetragonus (300 mg/L) as shown in Figure 8 (d), while a further increase in the coagulant dose gave no improvement. The future scope of the work also lies in possibility of modelling and optimization studies through Response Surface Methodologies for the bioformulations so developed29–31. Analysing biocoagulants on the basis of protein concentration A comparison of biocoagulant activity is possible on the basis of its protein concentration. The protein contents of the biocoagulants were determined by using the Thermoscientific Nano drop 2000c equipped with BCA(bicinchoninic acid) colorimetric assay to quantify the protein samples. The results are summarised in Table 3 and their coagulant efficiency in terms of protein content were analysed. It can be seen that protein concentrations were lesser in Cicer arietinum and highest in Acanthocereus tetragonus while the rest of the coagulants showed nearly same concentration (~7 mg/mL) of the proteins.



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Proteins have charged groups- consisting of charged amino acids and charged functional groups32 that has the potential for electrostatic interaction to neutralize the charge sites on the dye moieties to produce the neutral flocs. Several works have also reported proteins as coagulation active components in plant extracts. 33 In this regard, there have been varying opinions of researchers, where neither proteins, polysaccharaides, nor lipids but organic polyelectrolytes have been reported as the main coagulating agent. It appears that, it is difficult to designate some particular class of chemical constituents in plant extract for determining the coagulation efficiency. However, the evaluation of protein contents will provide useful information to researchers in intepretating and understanding coagulation efficiency. From Table 3, it is seen that the concentration of the protein in Cicer arietinum was lower than that in Acanthocereus tetragonus and this effect is reflected in huge differences in the retention time of 48 h and 20 h required for these coagulants to attain maximum removal efficiency. Moringa oleifera requires significantly less retention time of 30 min. Even though protein concentration in Acanthocereus tetragonus was high, the higher retention time can be attributed to smaller size cationic proteins and other non-proteinic organic component present in the plant material.28 The longer retention time may also be due to the method of extraction adopted in the present study, which was simple water extraction, where the crude extract has high possibility of organic plant tissue content that may inhibit the performance of coagulating active agents, besides the other reason for smaller size flocs. Jerri et al ,

34

referred the presence of coagulating proteins in Moringa oleifera seeds. The

cationic polyelectrolytes in Moringa oleifera were believed to play a predominant role in enmeshment by net-like structure type of mechanism and have ruled out charge neutralization, double layer compression; and bridging type as the active protein component are small in size.28 However, the role of cationic proteins in coagulation process in Moringa oleifera cannot be denied.


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Table 3 Comparison of biocoagulants on the basis of protein concentrations Biocoagulant

Protein concentrat -ion (mg/mL)

Optimum coagulant dose (mg/L)

Cicer arietinum

2.93

Moringa oleifera

6.78

Azadirachta indica(seed) Acanthocereus tetragonus (wet) Acanthocereus tetragonus (dried) Azadirachta indica (pulp)

Retention time (hr)

800

Initial dye concentra -tion (ppm) 500

SVI (ml/g)

48

Dye Concentra -tion reduction (%) 89

1560

50

0.5

99

41

3840

100

0.5

99

32

3840

500

0.5

55

46

6.96

1400

500

72

58

-

7.35

1218

50

20

84

42

1218

100

20

90

39

1218

500

20

97

48

9.29

1200

50

1

28

-

NA

15%

500

72

95

-

-

Analysing biocoagulants using FTIR FTIR studies for the crude coagulant extracts and sludge formed by the combination of dye moieties, with the respective coagulants were analyzed. The identification of functional groups, position and intensity of these groups in the sludge were studied through FTIR in order to understand the possibility of retention of biomolecular groups present in the extract or any chemical changes taking place after coagulation; apart from understanding the reusability and disposal factors of the sludge obtained. Cicer arietinum extract had a broad band peak at 578 cm-1 due to Fe-O band. 35 A very broad band extending from 3393-3400 cm-1 due to O-H stretching, C=O stretch occurring at lower wavenumber of 1653 cm-1 due to conjugation with C=C or phenyl group & C-O stretch at 1241 & 1277 cm-1 affirms the presence of carboxylic acid groups. Further, the strechings



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appearing at 1345 and 1547 cm-1 can be attributed to the presence of NO2 group in Cicer arietinum extract. The respective sludge had similar peaks like the crude, only with the shift in position and change in intensity eg. stretching due to C-H was observed in both the crude and sludge below 3000 cm-1, however, it was much broader in the sludge; polysaccharide band in the range 1023-1203 cm-136 in crude and 1228-1043 cm-1 in the sludge also indicate similar fashion. The peaks near 1544 and 1655 cm-1

37

also present in the crude Cicer extract,

an evidence of C=O stretching due to amide became more sharper in the sludge form which may be due to chemical interaction during the coagulation process. As observed, new additional peaks were not found in the sludge material, but due to the association of suspended materials with floc, the peak positions and intensity were affected. The weak band at near 1400 cm-1 due to bending vibrations of –CH3 and scissor vibrations of CH2 38 became further weaker due to molecular interactions with the suspension.

39

The wet form of

Acanthocereus tetragonus extract depicts a simple spectra consisting of a broad peak of hydrogen bonded O-H stretch at 3440 cm-1 followed by intense peak at 1635 cm-1 due to C=C alkene stretch and out of plane bending at 623 due to =C-H. The peculiar CH3 bending and scissor vibration of CH2 was also observed at 1409 cm-1. Again, the broad peak centred around 3377 cm-1 due to hydrogen bonded O-H band was also observed in the composite formed by combination of wet Acanthocereus extract and the suspended particles; with positional shift due to interaction with suspended particles. This O-H band is ascribed to alcohols functionality as it is accompanied by C-O stretching, vibration due to saturated tertiary alcohol group at 1165 cm-1 and saturated primary alcohol vibration at 1039 cm-1. The characteristic bending absorption due CH3 observed in the sludge was sharper. The sludge composite of wet Acanthocereus exhibited additional new peaks at 2917 and 2854 cm-1 due to asymmetric and symmetric stretching of C-H bond from methylene group respectively which may arise from fatty acids and lipids21. Also, almost all the absorption peaks turned


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sharper and prominent along with the introduction of new peaks which were non-existent in the crude sample due to incorporation of associated impurities into the matrix of wet Acanthocereus extract. A very prominent and the most intense peak of this spectra was the characteristic band at 1653 cm-1 along with a medium peak at 1545 cm-1 which related to the C=O vibration of primary amides. 40 The dried form of Acanthocereus powder coagulant and its respective sludge also showed the occurrence of similar functional groups. However, positional shifts to higher frequency were observed.

Cicer arietinum crude Cicer arietinum sludge

100

% Transmittance

% Transmittance

Moringa oleifera crude Moringa oleifera sludge

80 60 40 20 4000

3500

3000

2500

2000

1500

1000

120 100 80 60 4000

500

3500

3000

2000

1500

1000

500

1000

500

Wavenumber (cm )

Acanthocereus tetragonus crude(dried) Acanthocereus tetragonus sludge(dried)

Acanthocereus tetragonus crude(wet) Acanthocereus tetragonus sludge(wet) % Transmittance

% Transmittance

100

2500

-1

-1

Wavenumber (cm )

90 80

110 100 90

70 4000

3500

3000

2500

2000

1500

1000

500

80 4000

3500

3000

-1

Wavenumber (cm )

2500

2000

1500

-1

Wavenumber (cm )

Azadirachta indica crude Azadirachta indica sludge 100 % Transmittance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


80 60 40 20 0 4000

3500

3000

2500

2000

1500

1000

500

-1

Wavenumber (cm )

Figure 9. FTIR analysis of various bio-coagulants and their respective sludge.



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The coagulant extract from Azadirachta indica seeds indicated hydrogen bonded –OH stretching at 3350 cm-1, strong C=O stretch at 1748 cm-1 which appears along with C-O stretching at 1240 cm-1, representing the characteristic feature of ester linkage group in the extract. Absorption bands in the region between 3000-2800 cm-1 i.e. peaks at 2925 and 2861 cm-1 were attributed to the presence of hydrocarbon chains 41 due to C-H stretching vibration. The strong C=O stretch at 1748 cm-1 and the C-O stretching at 1240 cm-1 represent the characteristic feature of ester linkage group in the bio-cogulant extract while C-O stretching vibration due to tertiary alcoholic group in the extract was indicated by the medium band at 1159 cm-1. The weak peaks between 1600-1200 cm-1 were assigned to characteristics of lipids, lignins and amino acid fractions.21 Further, the characteristic bending absorption of methyl groups was indicated by the medium absorption band at 1450 and 1367 cm-1. A nearly broad and medium intense band at 1648 cm-1 indicates the presence of unsaturation due to alkene while the band at 724 cm-1 represents the peculiar CH2 rocking vibration. The sludge composite from Azadirachta flocs had lesser number of peaks, though similar to the crude sample and of lesser intensity. Positional shifts of 10-20 cm-1 were recorded for the –OH, CH, C=O and C-O stretchings. The peaks below 1000 cm-1 were almost negligible in the sludge.The FTIR spectra of crude Moringa oleifera and sludge composite were almost identical except for the intensity variations, with some overlapppings in the region of C-H stretching at 2933 and 2852 cm-1 and C=O stretching vibration ester at 1738 cm-1. Both crude and the sludge form of Moringa oleifera exhibited a broad and a wide band due to H-bonded O-H stretching and C=O stretching vibration which occurred in conjugation with highly intensified C=C stretching at 1656 cm-1. The characteristic nature of presence of ester group can be ascribed from the occurrence of sharp C=O stretching at 1738 cm-1 and C-O stretching absorptions occurring between 1000-1300 cm-1 i.e. peaks at 1230 cm-1, 1158 cm-1 and 1050


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cm-1. Further, the crude form of Moringa exhibited out of plane C-H bending vibrations below 800 cm-1 whose intensities decreased significantly in the derived sludge composite.

Monitoring Coagulation/flocculation by FBRM technique It is possible to evaluate coagulation behaviour on the basis on particle counts using FBRM technique. A 1 min period of agitation was provided before the coagulant addition to confirm the FBRM baseline and equilibration process. The coagulant was added at 1 min. During the first part, the colloidal particles are aggregated by cationic coagulants through charge neutralization. A continuous stream of aggregates sweeps across the probe, enabling the efficient detection and monitoring of the flocs by probe window. The first stage of detection provides the useful information about the flocculation mechanism and kinetics since efficient aggregation is the prerequisite for the success of coagulation and subsequent removal of sludge. The data obtained by FBRM have been shown in Figure 10 for evaluation of chord length distribution of flocs, formed by coagulation of Congo red (initial concentration of 100 mg/L) with inorganic coagulants; Aluminium sulphate, PAC, PAC SAB18 (40 mg/L each) at room temperature. Figure 10 also shows the coagulation behaviour in 100 mg/L of Congo red using optimal doses of 40 mg/L of iron (III) chloride, 900 mg/L Acanthocereus tetragonus and 2300 mg/L of Moringa oleifera coagulants respectively. It was clearly observed that counts of 5-23 µm were more in number, contributing to the increased number of counts in the solution ̴ 15, 120, 140 counts respectively. At time t=1 min i.e. immediately after the addition of coagulants to the dye solution a sudden increase in the chord length distribution can be observed due to initiation of flocs formation

42

. After an initial period of rapid mixing, a slow agitation allows the flocs to 27 ACS Paragon Plus Environment


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aggregate. This stage corresponds to an increase in the size of flocs and as a consequence, there is a decrease in counts obtained where the chord length increases. After 15 min of slow mixing (t= 21 min), agitation was stopped to allow settling of the flocs obatined. In this regime too, a small number of chord counts were observed. After 30 min of settling time (t= 51 min), no counts were observed for PAC SAB 18 and aluminium sulphate, but small number of counts were observed for PAC indicating incomplete settling. Chord length distribution of sizes ranging from1-5 µm and 5-23 µm were found to be playing a very important role in the increase in number of counts.

43

It was observed that inorganic

coagulants form very less number of visible flocs, confirming smaller size of flocs compared to bio-coagulants.

Figure 10. FBRM Chord length distributions for different coagulants 28 ACS Paragon Plus Environment

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For iron (III) chloride, initially floc size

Green Approach to Dye Wastewater Treatment Using Biocoagulants

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