Article pubs.acs.org/est
Qualitative and Quantitative Analysis of Volatile Constituents from Latrines Jianming Lin, Jackline Aoll, Yvan Niclass, Maria Inés Velazco, Laurent Wünsche, Jana Pika,* and Christian Starkenmann* Firmenich SA, Corporate R&D Division, P.O. Box 239, CH-1211 Geneva 8, Switzerland S Supporting Information *
ABSTRACT: More than 2.5 billion people defecate in the open. The increased commitment of private and public organizations to improving this situation is driving the research and development of new technologies for toilets and latrines. Although key technical aspects are considered by researchers when designing new technologies for developing countries, the basic aspect of offending malodors from human waste is often neglected. With the objective of contributing to technical solutions that are acceptable to global consumers, we investigated the chemical composition of latrine malodors sampled in Africa and India. Field latrines in four countries were evaluated olfactively and the odors qualitatively and quantitatively characterized with three analytical techniques. Sulfur compounds including H2S, methyl mercaptan, and dimethyl-mono-(di;tri) sulfide are important in sewage-like odors of pit latrines under anaerobic conditions. Under aerobic conditions, in Nairobi for example, paracresol and indole reached concentrations of 89 and 65 μg/g, respectively, which, along with short chain fatty acids such as butyric acid (13 mg/g) explained the strong rancid, manure and farm yard odor. This work represents the first qualitative and quantitative study of volatile compounds sampled from seven pit latrines in a variety of geographic, technical, and economic contexts in addition to three single stools from India and a pit latrine model system.
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INTRODUCTION The flush toilet widely used in developed countries is not sustainable and requires a disproportionate investment in infrastructure. Consequently, agencies that seek to end open defecation in emerging countries are focusing on developing various models of free-standing toilets. Ending open defecation will require an integrated approach, including education and the development of toilet facilities that are safe and attractive to use. One drawback of many free-standing toilets, particularly those used by large groups of people in a community block model, is the development of malodors resulting from degradation of human waste products. Understanding the chemical composition of odors generated by human waste products is a starting point for the development of relevant technologies that can prevent, eliminate, neutralize, or mask the offending odors. In this study, sampling methods were developed to analyze latrine malodors by using model systems. Subsequently, the volatile organic compounds (VOCs) in working stand-alone toilets in informal communities in South Africa, Kenya, Uganda, and India were sampled and analyzed. It was reasoned that such knowledge is essential to develop complete solutions for management of latrine stench. A review of the existing literature showed that researchers have undertaken the analysis of volatile components of human urine or feces for various purposes, such as diagnosis of human disease,1−4 metabolism studies,5 and malodor control.6−9 The complexity of the volatile constituents present in human urine © 2013 American Chemical Society
or feces requires the use of gas chromatography (GC) for separation prior to structure determination by mass spectrometry (MS). Various sampling methods, such as direct headspace injection with a gastight syringe, purge and trap, solvent extraction, and solid phase microextraction (SPME), have been used to trap and enrich the volatile components of urine or feces for GC−MS analysis.5,6,8,10−12 The types and amounts of volatile components in human urine or feces have been reported to vary among individuals, depending on their diets and state of health.3,5,9 A variety of carboxylic acids, aldehydes, ketones, alcohols, hydrocarbons, phenols, sulfur-containing compounds, nitrogen-containing compounds, and furans have been reported in human urine and feces.3,5,9 The malodor of human feces has been attributed to hydrogen sulfide, methyl mercaptan, methyl sulfide, dimethylsulfide, ammonia, trimethyl amine, formaldehyde, acetaldehyde, propylaldehyde, acetic acid, propionic acid, butyric acid, 3-methylbutyric acid, pentanoic acid, pyridine, and pyrrole.9 Sato et al. analyzed the volatile components of human waste samples, presumably consisting of human urine, feces, and kitchen wastes, collected from the storage tank of a sewage disposal plant.8 Fifty compounds were identified in the headspace, and the potential malodorous compounds were subjectively determined to be acetic acid, Received: Revised: Accepted: Published: 7876
April 18, 2013 June 18, 2013 June 21, 2013 July 5, 2013 dx.doi.org/10.1021/es401677q | Environ. Sci. Technol. 2013, 47, 7876−7882
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Figure 1. Diagram of various field latrine types.
min. The exposed fibers were desorbed in a GC−MS inlet at 250 °C for 5 min. SPME Sample Storage and Transport. For field sampling, conditioned and sampled SPME fibers were kept in laboratory-made assemblies for storage and transport; the SPME fiber needle was inserted into a clean capillary glass tube, both ends of which were sealed by two GC septa to limit the air surrounding the fiber and to prevent external contamination from entering the capillary glass tube to reach the fiber. The assembly was then placed in a glass test tube with a cap for physical protection. The glass tubes with SPME fiber assemblies were packed in a thermal bag with cold packs for shipping or stored in a freezer to minimize loss of analytes prior to analysis. Porapak Q Sampling of Volatile Constituents from Latrines. Porapak Q sorbent (75 mL) was cleaned with acetone (3 × 50 mL) and Et2O (2 × 50 mL) in a fritted Buchner funnel. The clean sorbent was then placed in a distillation trap and heated at 150 °C for 12 h under a flow of argon and the process was repeated twice. The cleaned and dried Porapak Q sorbent (500 mg) was weighed into 1 mL GC vials for storage and transportation. Before sampling, 500 mg of the sorbent was placed between two stainless steel rings mounted with a stainless steel grid in the center. This device was installed in latrine ventilation ports overnight (19 h). Sampled Porapak Q sorbent was then collected into a glass vial with a small funnel and brought back to the laboratory. Each sorbent sample was extracted with 2 mL Et2O (containing 2 μg of internal standard [IS]), and the extract was concentrated to 100 μL for GC−MS analysis. Solid Phase Extraction (SPE) of Volatile Constituents from Field Latrines Using Oasis HLB Cartridges. About 50 g of latrine sludge was collected in polyethylene plastic bags and diluted with about 200 mL of water. The bag was closed, shaken for homogenization, and stabilized in a plastic bucket. Sediment was allowed to settle for 30 min to 2 h. The top layer was decanted and filtered through cotton wool into a cup and the filtrate was pumped through a ceramic filter. The resulting clear yellowish solution (30 to 50 mL) was loaded on a conditioned Oasis HLB cartridge (6 g) using a hand-held balloon pump. Oasis HLB cartridges (6 g) were conditioned sequentially with Et2O (40 mL), EtOH (40 mL), and H2O/
propionic acid, butyric acid, 3-methylbutyric acid, pentanoic acid, hydrogen sulfide, methyl mercaptan, pyridine, pyrrole, indole, skatole, ammonia, and trimethylamine. The concentrations of these components in the samples were also determined. The study of VOCs that contribute to malodors has a long history in the fragrance industry. Recently, Troccaz et al. reported a detailed study of the smell of urine and the role of microorganisms in the generation of the VOCs responsible.13 However, the malodorous volatile components of human urine and feces combined and fermented under actual latrine conditions in various geographic locations and used by diverse groups of people has yet to be investigated. This is the focus of our work.
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EXPERIMENTAL SECTION Materials and Chemicals. For details of chemicals, see Supporting Information (SI). Model Latrine (New Jersey, U.S.). Twenty-liter HDPE buckets were filled with 2 L of water. Each bucket was used by one volunteer at home to collect urine and feces at least once daily for 7 consecutive days. During this period, the volunteers, three men and two women, consumed their normal omnivorous diets. The buckets were loosely covered and kept in secluded areas without temperature control until sampling. The contents in the model latrines of various ages were thoroughly mixed with a spatula and about 4 g of the resulting slurry was transferred into 20 mL headspace vials using plastic pipettes. The samples in the headspace vials were transported to the laboratory for SPME sampling. Field Latrines. Sludge samples collected from field latrine pits were weighed and diluted with water 2−4 times. About 4 g of the diluted sludge was transferred into 20 mL headspace vials, and the vials were transported to a place equipped with electrical outlets for SPME sampling. SPME Sampling of Volatile Constituents from Latrines. Samples in headspace vials were conditioned at 40 °C prior to SPME for 10 min using a digital heating block (VWR, Radnor, PA, U.S.). Conditioned SPME fibers were exposed to the headspace of the vials in the heating block at 40 °C for 30 7877
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Table 1. Odor Descriptions and pHs of the Latrines Sampleda site
type
pH
odor description: (a) latrine at site; (b) collected sludge
Durban
UD
6.5
(a) weak: phenol-like, horse (b) medium: horse, manure, styrax, asphalt
Durban
VP dry pit
5.5
Durban
VP wet pit
6.0
Nairobi
VP
6.0
Nairobi (Fresh Life)
UD
6.0
Kampala
VP
7.0
Kampala
VP
7.0
Pune A Pune B Pune C USA
single stool single stool single stool model system
7.0 5.0 5.5 9.0
(a) weak: sewage, phenol-like (b) strong rotten egg, sewage, rancid (a) medium: more sewage than fecal, rotten egg (b) strong rotten egg, sewage, rancid (a) strong: cheese, manure, horse, farmyard (b) strong: cheese, manure, ammonia, urine (a) weak: slightly urine, manure, rancid (b) strong, phenolic, rancid, manure, meaty (a) weak: farmyard, ammonia slightly urine, geosmin (earthy, moisture) (b) strong: rancid, rotten onion, phenylacetic acid-like (a) medium: farmyard, ambrinol (earthy, moisture), rancid (b) strong: rancid, phenolic, rotten vegetable strong: rancid, phenolic strong: spicy, cumin, phenolic rancid medium: cheese, curry, green stale urine, fishy, amine, hay-like, cresolic, honey sweet
a
comments sand was added. dry soft material. garbage. dark olive. wet slurry. plastic, garbage. gray liquid. water infiltrations. plastic, garbage. brown. full of white worms. sawdust added. brown, soft. wet pit, stools plus water. dry pit. yellow brown, soft. green, very soft. dark brown, greenish. brown heterogeneous suspension.
UD = urine diversion; VP = ventilated pit.
EtOH (9/1, v/v, 40 mL) in the laboratory and brought to the sites in plastic bags. On site, the cartridges were reconditioned with mineral water before sample loading. Sampled Oasis HLB cartridges and a blank cartridge were shipped back to the laboratory in separate plastic bags. In the laboratory, the cartridge was washed with water (40 mL) and eluted with Et2O (40 mL containing 40 μg of IS); the eluent was dried on Na2SO4, filtered, and concentrated using a small Vigreux column to 100 μL for GC−MS analysis. For details regarding GC−MS analysis, determination of SPE recovery factors at various pHs, single stool analysis, and the isotope dilution assay (IDA) of latrine malodor compounds by SPME, see SI.
In Durban, latrines were used by two or three families and emptied about every 2 years. The concrete receiving tanks of Durban ventilated improved pits were not fully waterproof. As a result, water could drain in or out, and pit latrines were reported to overflow during heavy rains. The pit latrines sampled contained various garbage, and the sludge was greenish gray. The odor of the sludge was typical sewage, methyl mercaptan, and rotten egg. In the proximity of the Durban UD latrines, there was a strong urine smell, slightly ammonia, and animalic, typical of urinals. Inside the UD latrines, the smell was weak, slightly urinal, and farmyard. The collected sample was quite solid and had a weak smell, most likely due to the sandy red soil added to cover newly added feces, and the odor was reminiscent of manure, styrax, and asphalt. In the Mukuru informal settlement in Nairobi, latrines were used by 30 to 50 persons per day. The traditional VP latrines were poorly maintained and were full of white worms. The ages of the sludge sampled from the VP latrines were not known. The odors of the collected sludge were strongly cheesy, manure, and farmyard. The Fresh Life latrines in Nairobi were a recently introduced model of UD latrine installed by Sanergy. These latrines were emptied every day and cleaned regularly. Between uses, the feces were covered with sawdust. No ventilation port was installed for these latrines and, even though they were clean, a typical barnyard, feces, cheesy, urinal odor was noticed at the site. In Kampala, the latrines were emptied about every 2 years. The Kampala VP1 pit was connected via a pipe to a plastic tank, and users washed their waste into the pit with water they carried in a drum. An odor reminiscent of farmyard, urine, and moisture was perceived inside and around the latrine, probably due to some people urinating outside the pit. The odor in the tank was strong, rancid, and phenolic. The sludge was quite compact without obvious moisture even though water was used in these toilets. The Kampala VP2 latrine was a small two-story building, and users climbed a ladder to reach the pit. The odor inside the latrine was described as farmyard, rancid, and earthy. The collected sludge smelled strongly rancid, phenolic, and rotten vegetable and was full of small black worms.
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RESULTS Odors Descriptions of Latrines Studied. Two types of latrines were sampled: those where feces and urine were collected together (Figure 1A) in Durban, South Africa, Nairobi, Kenya, and Kampala, Uganda having two distinctive designs (Figure 1A and B), and those where urine was diverted from the feces (Figure 1C, Durban and 1D, Nairobi), called urine diversion (UD) latrines. In Durban, the former latrines were referred to as ventilated improved pits, but at the other sites they were called ventilated pits (VPs). In Pune, remains of single stools were collected in public toilets. The odors of the latrine sites and collected sludge were evaluated and described by a perfumer and two scientists (Table 1), who were trained to smell and describe odors of single molecules and complex mixtures. The intensities were rated as weak when these individuals had to sniff attentively to describe the odor, medium when the odor was obvious but not repulsive, and strong when the odor was repulsive. In New Jersey, U.S., five model latrines were generated in buckets by five individual volunteers as detailed in the Experimental Section. The model latrines were sampled after 7 days, and the pHs ranged from 8.3 to 9.0. The odor descriptions of the model latrines varied: stale urine, fishy, amine, cresolic, honey sweet, and hay-like. 7878
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Many alternatives for VOC sampling exist,5,11,14 and a static headspace technique using Porapak Q was selected for this study. An advantage of the method is that the extracts could be olfactively evaluated in the laboratory. The results displayed in Table 2 clearly indicate that acids were not well absorbed due to the sludge pH. It was not realistic to carry volatile organic solvents to the field. SPE was a good alternative to liquid/liquid extraction and gave extracts for olfactive evaluation and multiple injections. The results in Table 2 show that highly volatile compounds were lost during the SPE protocol because of solvent evaporation. Phenol was also lost, probably because it is water-soluble. The only ester observed by SPE was ethyl 3hydroxybutanoate, which is an industrial contaminant, similar to phthalates and chlorobenzene derivatives, which were ignored in this study. In the field, it was realized that some sludge samples were very difficult to filter, particularly those from VPs in Nairobi and Kampala. Conditioning SPE cartridges, filtering sludge, and loading filtrate on the SPE could take longer than 1 h per sample. The SPE method was consequently not practical for large numbers of samples in the field. SPME was eventually selected for the comprehensive qualitative and quantitative study of the model and field latrines. Nevertheless, as shown in Table 2, analysis of Porapak Q and SPE extracts allowed us to identify a number of VOCs that were not observed in the SPME chromatograms. Analysis of Latrine VOCs: Comprehensive SPME Analysis. The GC−MS data files obtained from SPME GC− MS analysis of 16 latrines were analyzed using AMDIS deconvolution software. Only peaks with areas greater than 105 total ion counts were initially considered. In addition, peaks from the blank fiber background or from the spiked IS solution were not taken into account. In total, 198 different volatile constituents were detected among the 16 latrines investigated. The volatile constituents were identified on the basis of mass spectra (MS) and retention indices (RI) or by mass spectra alone. The occurrence of the volatile constituents detected in the 16 latrines are compared in Table S1 of the SI. If a volatile constituent was detected in a latrine, then the corresponding cell was filled with a different shade of blue, depending on the area of the peak. This representation provided an overview of the volatile constituents in all 16 latrines and focused attention on the most frequently occurring or most abundant latrine volatile constituents. Among the 14 nitrogen-containing compounds, indole was the most frequently occurring volatile constituent. It was found in almost all of the 16 latrines, including the two Durban latrines, where it was detected at much lower abundances. Skatole followed indole as the second most frequently detected volatile compound. Ammonia and trimethyl amine were found in all five model latrines but were not detected in any of the field latrines. Among the sulfur-containing compounds, dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide were detected in 10 or more latrines. Methyl mercaptan appeared as the next most frequently occurring compound. Carboxylic acids are an important class of latrine volatile constituents and acetic, propionic, isobutyric, butyric, isovaleric, 2-methylbutyric, pentanoic, and hexanoic acids were the main acids detected by SPME. Significant differences in carboxylic acid abundance were observed between the latrines, and in both types of Nairobi latrines, the concentration of butyric acid was between 0.1% to 1% of the sludge chromatogram.
In Pune, India, the pit latrines were aligned inside small cabins in a two-story concrete building as an amenity for the dwellers of the informal community in which they were located. Users carried a bucket of water to rinse urine and feces into the pits, which emptied into a nearby marsh or “river” through pipes. Three samples were collected from three individual fresh feces that had not washed away. The odors of the three samples were very different, as described in Table 1. Analysis of Latrine VOCs: Comparison of Three Sampling Techniques. The VOCs of a Nairobi VP detected by SPME were compared with the VOCs obtained by static headspace using Porapak Q and SPE. Table 2 shows that the Table 2. Comparison of Selected Volatiles Detected in Nairobi VP2 by GC−MS Using Three Sampling Techniquesa Nairobi VP2
Rt 3.99 4.35 5.36 6.09 8.03 8.46 9.72 11.47 11.98 12.99 15.13 16.06 16.12 17.64 18.05 18.17 18.63 20.49 20.71 21.02 22.66 23.71
name propanoic acid dimethyldisulfide 2-methylpropanoic acid butanoic acid 3-methylbutanoic acid 2-methylbutanoic acid pentanoic acid 4-methyl-pentanoic acid phenol hexanoic acid paracresol heptanoic acid nonanal 3-ethylbenzaldehyde benzoic acid 4-ethylbenzaldehyde octanoic acid phenylacetic acid 1-(3-ethylphenyl)-1ethanone indole 3-phenylpropanoic acid skatole
PORAPAK
SPE
SPME
occurrence
occurrence
occurrence
y y y
y
y y y y y y
y y y y
y y
y y y
y y y y y y y y y y y y
y y
y y y y
y y y
y y
a
SPE = solid phase extraction; SPME = solid phase microextraction; y = detected.
three VOC sampling techniques gave complementary results. SPME was the initial sampling method developed because the technique involved using a simple and portable device, which was particularly suitable for field sampling. In addition, SPME minimized scientists’ contact with the urine and feces, which is especially critical when handling potentially pathogen-carrying field samples. Samples collected on SPME fibers showed satisfactory stability when the SPME fibers were kept in a protected assembly and shipped chilled. However, SPME has several drawbacks: samples collected cannot be evaluated by smelling or injected for analysis multiple times, it is ineffective in the extraction of higher boiling volatile constituents, and the relative abundances of different compounds observed could be significantly different from their relative concentrations in the samples due to different partition coefficients between the fiber and analytes. 7879
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Table 3. Concentrations (μg/g) of 10 VOCs in 10 Latrines latrine Durban VP (dry) Durban VP (wet) Nairobi UD (Fresh Life) Nairobi VP Kampala VP1 Kampala VP2 Pune A Pune B Pune C model latrine a
dimethyl sulfide
dimethyl disulfide
dimethyl trisulfide
butyric acid
3-methyl butyric acid
2-methyl butyric acid
phenol
pcresol
indole
skatole
0.027 0.020 0.11 0.10 0.057 0.059 2.1 1.6 0.078 0.060 0.033 0.031 0.33 0.41 0.11 0.11 0.026 0.022 0.47 0.50
NDa NDa 0.12 0.04 0.080 0.093 2.3 2.5 0.10 0.05 0.031 0.058 11.9 9.0 0.0058 0.0052 0.071 0.072 0.051 0.049
NDa NDa 0.003 0.001 0.004 0.017 2.1 0.9 0.004 0.010 0.0014 0.0022 1.2 0.6 0.0011 0.0010 0.015 0.014 0.008 0.011
116.1 91.0 120.3 207.1 1027.2 1042.0 6658b 13578b 63.3 49.8 51.2 46.2 493.7 538.0 507.8 537.0 710.3 726.6 865.2 982.9
11.0 6.2 25.6 18.6 239.1 236.3 428.7 440.7 17.2 13.9 27.4 25.1 112.5 119.9 8.2 9.3 92.5 85.7 149.9 151.2
2.9 4.4 15.9 18.3 187.9 190.5 297.7 297.0 9.0 8.0 19.8 20.3 82.8 99.7 1.0 1.3 46.5 43.6 144.0 153.5
0.60 0.55 0.50 0.66 0.58 0.57 13.5 13.7 1.7 2.4 5.6 5.5 0.3 0.3 0.60 0.50 1.7 1.8 14.1 12.8
0.010 0.022 0.53 ND 37.7 42.7 54.3 89.3 6.9 7.8 4.2 3.8 18.8 23.7 0.10 0.11 7.4 8.0 63.2 62.5
0.44 ND 0.47 0.19 9.0 9.5 120.5 65.4 3.8 5.9 3.7 3.3 6.8 9.6 3.8 4.5 20.3 22.9 5.3 3.9
0.10 0.12 0.47 0.29 5.4 5.3 9.0 5.8 2.0 1.9 3.7 2.8 4.4 5.8 0.027 0.049 0.6 0.7 6.7 5.7
Not dectected (ND). bUnderestimated due to saturation.
Phenol and p-cresol were both the most frequently occurring and the most highly abundant compounds. Other compounds detected by SPME are listed in Table S1 of the SI. Quantification of 10 Selected Malodor Compounds from Latrines. To gain a better understanding of the differences between the volatile constituents of different latrines, we determined the accurate concentrations of 10 potential malodor compounds in latrine sludge samples. The 10 compounds that were selected represented the four classes of chemicals believed to contribute to latrine malodor and were ubiquitous in most latrines. SPME with an isotope dilution assay (IDA) was the method of choice because SPME is especially suitable for field sampling and its limitation in quantitative analysis can be overcome by the use of isotope labeled IS.15−17 An IDA method for the 10 selected compounds was therefore developed (see SI for method development). The IDA method was used to determine the concentrations of 10 selected VOCs in nine field latrine samples and the results are listed in Table 3, along with those from a model latrine. Significant interlatrine variations in the concentrations of all 10 VOCs were observed. The concentrations of the 10 compounds were the lowest in the two Durban latrines, followed by those of the Pune and Kampala latrines, while those of the two Nairobi latrines were the highest. Among the four classes of compounds quantified, the concentrations of the three sulfur compounds were the lowest, while those of the three carboxylic acids, especially butyric acid, were the highest. However, the levels of the sulfur compounds were exceptionally high in the Nairobi VP and in Pune A. The levels of the two phenols and the two N-containing compounds fell in between these extremes. Evolution of Malodor Compounds in a Single Stool from a Latrine. To gain a preliminary understanding of the variations in VOC concentration that were observed, we studied the evolution of malodor compounds in two single feces samples. The concentrations of indole, skatole, p-cresol, and six carboxylic acids in the samples were determined over 7
days using an SPE method. The evolution of the concentrations of nine selected malodor compounds in the two single feces samples at 22 °C is shown in Figure 2 (A and B).
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DISCUSSION This work represents the first effort to compare latrine VOCs from different groups of people in a number of different countries. To prepare for this project, we studied model latrines
Figure 2. Evolution of VOC concentrations in two stools A and B over 7 days: (A) acids and (B) p-cresol, indole, and skatole. 7880
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of butyric acid, which were similar among the three samples, did not appear to correlate with this perceived difference (Table 3). But the concentrations of 2-methylbutyric and 3methylbutyric acids were much higher in samples A and C, where the butyric and rancid odor was intense, compared with sample B, where no butyric note was perceived. The lower pH of sample C (pH 5.5) than of sample A (pH 7) could explain the more intense butyric note perceived in sample C, despite the lower relative concentrations of the two methylbutyric acids. The Nairobi (Fresh Life) and India samples consisted entirely of fresh stools; consequently, a study was undertaken to understand the VOC differences between fresh stools and sludge containing aged material. Figure 2 (A and B) shows the evolution of VOCs in stools over 7 days. The concentrations of six acids (Figure 2A), as well as skatole, indole, and p-cresol (Figure 2B), were monitored over time. The concentrations of the acids decreased and after 7 days, only about 20% of the initial concentrations remained. It can be postulated that the rancid, vomit, noxious odor of fresh feces will decrease with time. It was also observed that p-cresol increased almost in inverse proportion to the acids; this indicated that the barn or farmyard smell became dominant over time. The concentrations of indole and skatole did not vary over time; therefore, the fecal malodor impact of these molecules remained constant. This study represents a significant advancement in the development of an understanding of the VOCs in free-standing latrines under different environmental conditions. As expected, different latrines contained VOCs from common chemical classes, and there was significant overlap in the VOCs identified. Differences that were observed in the odors and VOC profiles can be attributed to the age of the waste, storage conditions, and whether urine was mixed with the feces.
in order to develop robust analytical methods and a better understanding of latrine VOCs. The field latrines for this project were selected to represent diverse geographic conditions, including wet and dry climates, but with a focus on free-standing latrines in informal settlements where solutions for malodor control are needed as part of an integrated solution to eliminate open defecation. Traditional (Figure 1A) and prototypical next-generation latrine systems (Figure 1B−D) were sampled to understand the diversity in the VOCs generated. Ten field latrines were sampled in four countries located on two continents, Africa and Asia. In Africa, Kampala and Nairobi are considered to be wet environments, whereas Durban is generally considered to be a drier climate. Our results indicate that the influence of climate was less important than the toilet design. For example, in Durban, some latrines were located below the water table and flooded in heavy rains (Durban Wet Pit, Figure 1). The sludge was consequently stored under anaerobic conditions and the odor was sewage-like, eggy, and methyl mercaptan. In Kampala, however, the pit latrines we visited were above the ground, where they were well protected from rainfall, and the odors of the latrines were farmyard, ammonia, and rancid. In the latrines shown in Figure 1B, a small volume of water was typically used to wash away the waste. The amount of water used was not enough to cover the sludge. The composition of volatile constituents differed between latrines (Tables S1 of the SI), and VOC concentrations in the sludge varied significantly (Table 3). De Preter et al.5 suggested that latrine VOC variations probably reflect differences in dietary habits and gut microbiology. In the case of pit latrines, however, many other parameters, including frequency of emptying, design, and drainage, most likely played important roles in the observed odor and volatile composition differences. As expected, on the basis of the VOC profiles, latrine odor profiles and intensities differed between sites (Table 1). Correlating these latrine odor characteristics with the volatile constituents collectively found in the latrines in Table S1 of the SI, it can be postulated that the latrine odors were mainly due to four classes of chemicals: nitrogen-containing compounds, including indole and skatole; sulfur-containing compounds, such as methyl mercaptan and dimethyl-di(tri) sulfide; carboxylic acids; and phenols. Odor-causing compounds from a commercial dairy farm were recently identified to be phenol, p-cresol, 4-ethylphenol, indole, skatole, benzyl alcohol, valeric acid, isovaleric acid, and hexanoic acid.18 Therefore, the manure, farmyard, horse-like characteristics of latrine odor likely resulted from the combined effects of phenol, p-cresol, indole, skatole, and some carboxylic acids. The carboxylic acids, including isobutyric, butyric, isovaleric, 2-methylbutyric, valeric, hexanoic, and phenylacetic acid, likely caused the rancid, cheesy characteristics of the latrines. The methyl sulfides, such as dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, methyl mercaptan, and H2S, are known to give sewage, rotten egg, and rotten vegetable odors.19 From this comparative study, our conclusion is that when the pit latrine contained water, anaerobic fermentation produced sewage-type odors; in pit latrines where the feces dominated, the rancid odor was predominant; and in the case of UD toilets, the farmyard odor was more present. In the model latrine system, the degradation of urine led to the fishy ammonia odor produced mainly by trimethyl amine.20−22 Among the three Indian samples, pronounced differences in rancid malodors were perceived (Table 1). The concentrations
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ASSOCIATED CONTENT
S Supporting Information *
Descriptive texts and tables of experimental procedures. This material is available free of charge via the Internet at http:// pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Tel: +1-609-580-6876; e-mail: Christian.starkenmann@ firmenich.com(C.S.), Jana.Pika@firmenich.com (J.P.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Our appreciation to Dr. Carl Hensman, program officer of the Bill & Melinda Gates Foundation, for guidance in the field; Prof. Chris Buckley of The University of KwaZulu-Natal and his team for lab support; Ani Vallabhaneni and Florence Mwikali Musyoki of Sanergy for support in Nairobi; Frank Millsop and Isaac Namkoola of Water for People for support in Kampala; and Raj Iyer and his team at the Mahindra Pride School, the Naandi Foundation, for support in Pune. We would also like to thank Haresh Totlani from Firmenich India, as well as the perfumers Makarand Kamat and Gary Marr for support in India and Africa, respectively.
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ABBREVIATIONS (VOCs) Volatile Organic Chemicals 7881
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Environmental Science & Technology (SPME) (SPE) (IS) (IDA) (UD) (VP) (GC) (MS) (PDMS) (CAR) (DVB) (HDPE)
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Article
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Solid Phase Microextraction Solid Phase Extraction Internal Standard Isotope Dilution Assay Urine Diversion Ventilated Pit Gas Chromatography Mass Spectrometry Polydimethylsiloxane Carboxen Divinylbenzene High Density Poly Ethylene
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dx.doi.org/10.1021/es401677q | Environ. Sci. Technol. 2013, 47, 7876−7882
