Tre
e SEDIMENTATPON AND SLU GE HANDLING AUGUST S. ERSPAMER AND WILLIAM D. RICE P . H . Glatfelter C o m p a n y , Spring Grove, P a .
At
present there is no standardized method for the treatment of wastes from semi-integrated pulp and paper mills. This paper describes the pilot plant equipment, the operating procedures, and the studies carried out to obtain information on sedimentation and sludge handling which could be applied to a process for treating such wastes. The pilot plant has bcen a satisfactory demonstratioii unit and the data obtained have been utilized as a basis of design for a proposed treatment works.
T
treatment. These are the mill main effluent wastes which include the chlorination and caustic extraction stage washer filtrates in the bleach plant, de-inking washer d i d l a r g e , paper machine losses, and general wash-ups. To determine whether the treatment works could be technically and economically justified, a pilot plant Tvas constructed and p u t in operation in January 1948. The general program layout was developed cooperatively by the mill technical staff, the Katiorial Council for Stream Improtemerit, and engineeis from the Stato Sanitary Water Board. The purpose of this paper is t o describe the pilot plant cquipment, the operating procedure, and the studies carried out to obtain information on sedimentation and sludge liaridling which could be applied to a process for treating the wastes requiring outside treatment.
HE pollutional effects of an industrial waste on a stream, aside from appearancr, are due t o bulk solids, which settle out and cause deposits in the stream, suspended matter, and soluble materials. Substances present in the pulp and paper mill wastes include fiber, fillers, soluble oxidizable materials, salts, and pulp processing rejects such as knots, screening rejects, I’PLOT P L A N T EQUIPRIENT spent cooking, de-inking, and bleaching liquors. The pilot plant was built in the open near the main emuen& The treatment of pulp and paper mill wastes, with the exchannel. Figure 1 gives the layout of the equipment, and a ception of the established chemicals recovery systems for sulfate schematic flow sheet of the process is presented in Figure 2, and soda pulping residual liquors, is not standardized because The plant is shoxvn in each mill has its own Figure 3 with the setSLUDGE problems which must he ENCLOSEL C O F l T R O L R O O M HOLDING tling- tank on the left dealt k i t h individually. and the flocculating tank The most effective and o n the right. usually the least cspenI VACUUM FILTER 1 Pump for Waste sive methods of waste Supply. The waste was disposal are preventive pumped from the main nieasures applied a t the EOUIPMENT effluent channel to thc source, Any reduction :ILTER HOUSE pilot plant a t the rate of solids discharged to of 2 0 0 g a l l o n s p e r the stream, t h a t is niinute by a BO-foot effectcd by careful and head centrifugal pump. improved mill operation, SETTLING A 3 - f o O t square bur TANK results in a direct benescreen mith 0 . 2 5 - i n c h fit to the stream. Howbars spaced on 0.75-inch ever, even after reduccenters successfully kept tion of pollutional load the pump operating with to a minimum inside the a minimum of clogging. mill by improvements in Selector Flume. ELEVATED PLATFORM equipment and operaThe wooden s e l e c t o r tions, there remains a f l u m e , a p o r t i o n of large - volume of wastes w h i c h s e r v e d 8s t h e which require outside Figure 1. Floor Plan of Waste Treatment Pilot Plant 1806
1
LIIII I l l I I I I I I I111111111l11 l l I I I I I
August 1949
INDUSTRIAL
AND E N G I N E E R I N G C H E M I S T R Y
1807
flocculation tests. The waste was admitted at the bottom and discharged through a n outlet near the top of the tank. Gentle mixing was provided by a paddle agitator moving at a peripheral speed of 1 foot per TO STREAM second; a throughput of 84.5 gallons per minute gave a detention time of 19 minutes. This tank and the flash mix tank were by-passed during the INFLUENT plain settling tests by using the line 1 running directly from the 3-inch VenWASTE turi flume t o the settling tank. Settling Tank. The circular settling tank (Figure 4), a wooden stave tank 14 feet in diameter and 14.75 feet deep, was fitted with a 45' sloped cone bottom. The effective settling depth and retention volume were 11.23 feet and 10,100 gallons, respectively; a 2-hour detention time was attained at a throughput of 84.5 gallons per Figure 2. Schematic Diagram of Waste Treatment Pilot Plant minute. The baffled submerged inlet was at the center of t h e tank and the submerged outlet at the perimeter was equipped with a scum baffle. The tank was provided with stilling box, was equipped with an adjustable gate which regudecanting pipes to remove the supernatent waste at the end of a lated the amount of waste treated; the unused portion was returned t o the main effluent. run prior t o withdrawing the sludge. The hopper bottom of the Venturi Flume. The 3-inch Venturi flume, constructed of settling tank had a holding capacity of 2650 gallons. It served stainless steel sheet metal, measured the volume of waste treated, as a collector for the settled sludge which was drawn off by gravity and chemicals, when called for, were added a t the flume discharge to the measuring tank. by means of a constant level orifice box. Sludge Measuring Tank. The sludge measurements were Flash Mix Tank. A 50-gallon closed wooden barrel with the carried out in a wooden tank 5 feet in diameter by 4 feet deep. Experimental Vacuum Filter. A 1 X 1 foot rotary vacuum inlet at the bottom and the outlet near the top gave rapid and complete mixing of the waste and chemicals in the chemical filter (Figures 5 and 6), covered with a 60 X 40 mesh stainless flocculation tests. steel wire cloth, was employed for the sludge dewatering tests. The filter had a total filtering area of 3.14 square feet and was opFlocculation Tank. A wooden tank, 6 feet in diameter and 6 feet deep, was employed for both the mechanical and chemical erated at a vacuum of 25 t o 27 inches, with 25% submergence.
Figure 3. Waste Treatment Pilot Plant
1808
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No. 8
time available. The vacuum filter vms et,a.rted up on the 6minute cycle and approximately 15 minutes were required to attain equilibrium conditions. After sampling, the filter was speeded up t o the 2.25-minute cycle and 10 minutes r e r e allo~ved t o build up t o equilibrium conditions. COLLECTION OF DATA
The pilot plant program was divided into t n o phases, sedimentation and dudge liaridling. The sedimentation tests covcrrd plain settling, with and without meehaiiical flocculation (no chemical addition), arid settling aided b> chemical treatment,
TABLE
Figure 4.
Waste Treatment Settling Tank
OPERATION O F THE U S I T
The pilot plant v a s operated by three members of the niill ehemical engineering staff under the control of the technical director. The unit was operated oii a oiie-shift basis for a 5-day n-eelr during the sedimentation phase of the studies. HorT-ever, In order to obtain enough sludge for the vacuum filter tests, it, was necessary to put the settling ‘unit on 3-shift, 23-hour-per-day operation. In starting up the plant approximately 2 hours wwe required to fill the system n-ith Trast,e and attain equilibrium conditions. The runs were then continued for 4 to 7 hours, the longer runs being carried out at the highcr dct,ention periods. The average length of run in the rotary vacuum filter tests was 0.5 hour. This was chosen as the most practical because of the number of variables nhich had t o be covered and the necessity t o include as ninny different sludges as possible in the
Figure 5.
I.
PLAIS ~EUIXE~~TATIO OF X
Detention time, hours No. of runs Settleable solids Influent, d / l . Effluent, m1,Il. Removal, yo Suspended solids Influent, p.p.m. Effluent, p.p.m. Removal, yo Turbidity Influent, p.p.m. Effluent, p.p.m. Removal, 7’’
PH
Influent Effluent Color Influent, p.p.m. Effluent, p.p.m. Removal, % B. 0 . D. Influent, p.p.m. Effluent, y.p.m. Removal, % Sludge Concentration, Ash, 7c Loss on ignition, ’%
Experimental Rotary Vacuum Filter
XILLWASTES
1
2
4
10
10
10
32 1.0 97
30 0.7 98
27 0.2 90
623 113 82
74.* 90 86
628 76 88
212 101 53
266 96 63
212 77 64
7.$ 7.5 290 278
9.0 8.8
8.0 7.8
4
260 250 0
270 260 3
164 139 16
146 124 16
157 15
3.7 40 60
4.2 44 56
1%
3.0 41 59
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
August 1949
1809
of each’run. When the filter had reached equilibrium operation, samples of the filter cake and filtrate were obtained. Imhoff cone tests were performed on mixtures of mill waste and sludge filtrate t o determine effects of filtrate addition on mill waste settling characteristics. OBSERVATIONS AND R E S U L T S
The results of plain sedimentation are summarized in Table I. A high reduction in settleable solids volume was effected by plain settling, with detention times in the range of 1t o 4 hours exerting
Y
Figure 6.
V a c u u m Filter in O p e r a t i o n
using alum and pickling liquor. The test runs mere 6, 7, and 9 hours in length for detention times of 1, 2, and 4 hours, respectively. I n the plain settling tests, ten repeat runs were carried out under each set of conditions. The chemical coagulation tests were exploratory in nature with only one or two runs being made a t each of the test conditions. Two composites of t h e influent and effluent wastes, consisting of samples collected every 15 minutes, were made for each run. One influent (or effluent) composite represented the first part of the run and the other composite the last part of the run. The supernatant waste in the settling tank was decanted down t o the to the sludge level at the end of each run and the sludge was withdrawn t o the sludge measuring tank. The volume of sludge was then recorded and a sample taken for analysis. The analyses carried out are covered in standard methods (1). Sludges obtained by plain settling were filtered on the rotary vacuum filter with and without sludge conditioning and/or compaction. The investigation covered the general characteristics and filterability of plain settled sludges and the effects of sludge conditioning and/or compaction. The chief materials used for sludge conditioning were lime and carbon; the latter were derived from the pulp mill recovery system. A total of 134 filter runs were made on 65 different sludges with approximately 30 gallons of sludge being used for each test. Filtering cycles of 2.25 and 6 minutes were employed; the average length of run was 0.5 hour. Average samples of the thoroughly mixed sludge were taken from the sludge holding tank at the beginning a
TABLE11. EXPERIMENTAL ROTARYVACUUM FILTER TESTSUXCONDITIONED SLUDGES
Sludge Concentration Range, % Average, Yo Ash, % Loss on ignition, % 2.25-minute filter cycle KO.of. tests Filter cake Lb./sq. ft./hr. Moisture, % Thickness, In. Filtrate, gal./sq. ft./hr. &minute filter cycle No. of tests Filter . .... c.n -k..n.
Lb./sq. ft./hr. Moisture, 7” Thickness In. Filtrate, gal.l/sq. ft./hr. Filter cake (composite) Ash, % Loss on ignition, % Filtrate (composite) Suspended solids, p.p.m. Val. suspd. solids, g.p.m.
2.0-2.9 2.5 40 60 3 2.9 75 2/32 12.6 8
3.0-3.9 3.5 39 61
16 3.2 76 3/32 9.7 17
4.0-4.9 4.4 41 59
6 4.3 78 5/32 9.8 9
5.0-5.9 5.7 45 55 1 5.2 71 6/32 8.8 1
1.2 72 3/32 5.0
1.7 72 4/32 5.1
2.3 72 7/32 5.3
3.9 65 8/32 6.9
39 61
38 62
41 59
50 50
82 1 394
733 300
901 379
1530 733
only a small effect. The over-all turbidity removal averaged 60% and the suspended solids reduction 85%, being 82, 86, and 88% for 1-,2-, and &hour detention times, respedtively. Mechanical flocculation was found t o exert very little, if any, iiifluence, The 5-day B.O.D. reduction averaged 15% for all the runs and differences in pH and color of t h e waste before and after treatment were negligible. The sludges obtained had an average concentration of 3.6% and on analyses gave an average of 42% ash and 58% loss of ignition. The chemical flocculation runs, which nere exploratory in nature, indicated that the only significant change brought about by the addition of cliemicals was a 60% reduction in color of t h e waste when approximately 400 p.p.m. of alum were used. Pickling liquor, on the other hand, tended to increase the color of t h e effluent from the pilot plant Loadings ranging from 1.2 to 5.2 pounds of dry solids per bquare foot per hour were obtained (Table 11) when sludges produced by plain settling were filtered on the enperimental rotary vacuum filter. It was found t h a t concentration of the sludge had a decided effect on the loadings attained; higher concentrations resulted in increased loadings. On the average, higher loadings were obtained with the 2.25-minute cycle, b u t the resulting cakes were wetter and, a t times, difficult t o remove. Cakes produced a t the 6-minute cycle were generally dryer, thicker, and more handleable. Sludge conditioning studies covering 15 runs indicate that a n increase in net loadings up to 45% was realized through the use of lime (flocculant) or carbon (inert filter aid). -4pproximately 25% increase in loading was obtained by 24-hour compaction of the sludge. The characteristics of the filtrate from the rotary filter were similar t o the raw waste. Imhoff cone tests demonstrated that filtrate addition t o the raw waste had very little effect on settling characteristics, changes in settleable and nonsettleable solids being insignificant, APPLICATIOY OF RESULTS
The pilot unit has proved satisfactory as a source of design data for a full scale plant. On the basis of pilot plant operation and data, the company filed a preliminary report covering basic design data and sketch drawings of a proposed method of waste treatment with the Sanitary Water Board of the State of Pennsylvania. The board approved the plans, and the next step will be a, final report and plans for a full scale treatment works as outlined in the preliminary report. ‘
ACKNOWLEDGRIENT
The authors wish to acknowledge the assistance rendered by the National Council for Stream Improvement in the sedimentation phase of studies and by Oliver United Filters, Inc., in making available the experimental rotary vacuum filter. LITERATURE CITED
(1) American Public Health Association, “Standard Methods for Examination of Water and Sewage,” 9th ed., 1946. RECEIVED October 1, 1948. Presented before the Dlvmon of Water, Sewage, and Sanitation Chemistry a t the 114th Meeting of the AMERICAN CHsnricar. SOCIETY, St. Louis, Mo.
