The effects of organotin on the activated sludge process

Water Res. Vol. 18, No. 5. pp. 535-542. 1984 Printed in Great Britain. All rights reser',ed

0043-135484 53.00+0.00 Copyright ~ 1984 Pergamon Press Ltd

THE EFFECTS OF ORGANOTIN ON THE ACTIVATED SLUDGE PROCESS Y. ARGAMAN*,C. E. HUCKSt and S. E. SHELBY JR AWARE, Inc., Nashville, TN 37027, U.S.A. (Received February 1983) Abstract--Organotin compounds which find increasing use in marine antifouling paints may be present in the discharge from dry dock operations. This investigation was aimed at determining the effect of such wastewater when discharged to a municipal activated sludge treatment plant. Experiments were conducted using a Warburg respirometer and continuous flow bench-scale activated sludge systems. The results showed that unacclimated biological cultures can be inhibited by tributyl tin oxide (TBTO TM)concentrations as low as 25tlgl -~. However, TBTO doses of over 8000#gl -~ can be tolerated by a well acclimated culture. Continuous loading of up to 1000 #g I-~ TBTO had no effect on organic removal in activated sludge systems. However, an adverse effect on sludge settleability was noticed at 1001tg 1 - I TBTO. Shock loadings of 500 and 1000/~g I -I TBTO had no effect on soluble organic removal but resulted in impaired settling and higher effluent suspended solids. The LC_~0of TBTO to the fathead minnow was estimated at 45-200 ~g 1-~. The toxicity was reduced considerably by activated sludge treatment. Key words--organotin, tributyltin oxide, activated sludge, bio-inhibition, continuous loading, transient loading, toxicity

INTRODUCTION The unique properties displayed by tri-organotins, particularly tributyl and triphenyl-tin derivatives have led to a considerable increase in their use in marine antifouling paints. At the end of the useful life of an antifouling paint, the remaining paint is removed by wet abrasive blasting in a drydock. Wastewater generated during these operations may contain approx. 1001~gl -~ of organotin compounds. The maximum discharge concentration is estimated at 500 # g l -t. Since drydock facilities servicing ships do not generally operate extensive waste disposal systems the wastewater could be discharged to a local municipal wastewater treatment facility. The presence of the residual organotin, depending on its effects, may limit such a discharge by damaging the effectiveness of the municipal treatment plant and/or seriously increasing the toxicity of the treatment plant effluent. The prime biocide in such antifouling paints is tributyl tin oxide (TBTO), which is present as the cis isomer of (CH3CH,CH2 CH2)s-Sn-O-Sn-(CH.,CH.,C H,CH3) 3. The general objective of this investigation was to evaluate the effect of T B T O on the performance and operation of an activated sludge system treating municipal wastewater. The goals of the study were to: *Present address: Technion Israel Institute of Technology, Haifa, Israel. "['Present address: Post, Buckley, Schuh & Jernigan, Inc., P.O. Box 150214, Nashville, TN 37215, U.S.A. TBTO is a registered Trademark of M & T Chemicals, Inc. 535

(l) Determine the degree of inhibition imparted by T B T O on acclimated and unacclimated activated sludge. (2) Compare the response of acclimated and unacclimated activated sludge systems to transient loadings of TBTO. (3) Determine the degree of inhibition imparted by T B T O at twice the maximum projected concentration. (4) Evaluate the degree of detoxification achieved by activated sludge treatment of TBTO-laden wastewater. PREVIOUS STUDIES The relationship between molecular structure and toxicity of organotin compounds was discussed by Smith (1978). It was usually found that the triorganotin compounds, i.e. those in which the tin atom's coordination number is four, with three organic and one anionic group attached to it, are most toxic, are persistent in the environment, and are therefore well suited for use in marine antifouling paints. The c o m p o u n d used in this study, TBTO, belongs to this category. In tin compounds, the nature of the organic group has a marked effect on the toxicity while the anionic radical is not as important. N-butyl organotins have the most profound effect on such organisms as gram positive bacteria, fungi, molluscs and fish. This indicators that T B T O can be expected to affect the performance of activated sludge systems and, if not degraded in the treatment plant, may affect higher forms of aquatic life in the receiving water.

536

Y. ARGAMANet al.

The work of Slesinger a n d Dressier (1978), later summarized by Slesinger (1979), describes the fate o f three o r g a n o t i n c o m p o u n d s u n d e r various environmental conditions. In W a r b u r g respiration studies biological activity was observed at T B T O concentrations of up to 1 0 m g [-t. A n initial lag phase was noticed at 10rag l - ' but n o r m a l biological activity was rapidly restored by acclimation. The biod e g r a d a t i o n of T B T O was studied in a n o t h e r experiment showing 20 a n d 13.0,~, d e g r a d a t i o n of T B T O in 126 days at initial c o n c e n t r a t i o n o f 10 a n d 1.0 m g l -t, respectively. Stein and Kuster (1977) studied the effect of trio r g a n o t i n c o m p o u n d s o n the activated sludge process. They f o u n d that tributyl tin fluoride ( T B T F ) was inhibitory at 5.0 m g I -~ a n d T B T O at 10 mg 1-~. In transient shock loading 2.0--5.0mgl -~ T B T O caused a m a r k e d d r o p in B O D removal when applied to an unacclimated system. S u b s e q u e n t shocks had a lesser effect as the system became acclimated to TBTO. Polster a n d Halacka (1971) concluded that tributyl tin chloride (TBTC) has a bacteriostatic limiting value o f 1.0-5.0 mg 1-t a n d a bactericidic limiting value of 5.0-10.0 m g l -~. B o k r a n z a n d Plum (1971) found the inhibitory threshold level of T B T F to various bacteria between 0.2 and 3.1 mg 1-~. According to Slesinger (1979) the 96-h LCs0 o f T B T O to channel catfish is 0.012 mg ] -t. Schatzberg and Harris (1978) estimated the 24-h LC~o to guppy fry at 0.010-0.020 mg 1-~. Test results o b t a i n e d from the EPA A n i m a l Biology L a b o r a t o r y in Beltsville, M a r y l a n d report an LCs0 for T B T O to bluegills o f 6-13 mg 1-~.

The reactors were controlled to simulate steady-state operation of continuous-flow activated sludge units. Air was supplied to the reactors by diffuser stones and mixing was accomplished with small, variable-speed, propeller-type mixers. Each reactor contained an integral clarifier with an adjustable baffle to control sludge return. A schematic of the experimental setup used is presented in Fig. I. For the continuous loading phase of the study, the three biological reactors were designated as: Unit C, Zero organotin load control system. Unit I, Low organotin load test system. Unit II, High organotin load test system. The control reactor was fed only domestic sewage and served as the basis for evaluating organotin effects on the other two reactors. The sewage fed to the other units was spiked with organotin. Unit I was held at a lower organotin loading than Unit II in order to provide a safety margin for evaluating organotin effects. Had the biological population of Unit II been killed or severely inhibited, Unit I contained an acclimated bacteria for continuing the study. For the transient loading phase of the study, the three biological reactors kept their continuous-flow labels but the designations were modified as follows: Unit C, Zero organotin transient load, unacclimated seed control. Unit I, Organotin transient load test unit, unacclimated seed. Unit II, Organotin transient load test unit, acclimated seed control. Two transient loading tests were conducted after the completion of continuous-flow testing. Since Unit II had shown no significant deterioration through the continuousflow tests, it was chosen to serve as an acclimated seed control. Sludge from Unit I was discarded. Unit I was dismantled, cleaned and reseeded with a mixture of sludge from the original control Unit C and sludge from the domestic treatment plant used in the study. The sludge mixture was added to Units C and I. The method produced an unacclimated unit for control (no transient load), an unacclimated unit to receive a transient load and an acclimated unit to receive a transient toad.

EXPERIMENTAL Two types of experimental tools were employed in this investigation: (a) Warburg respiration tests, and (b) continuous-flow activated sludge systems. The Warburg tests were used to assess the acute effects of various TBTO concentrations on biomass of varying degrees of acclimation. The continuous-flow units were designed to simulate the performance of a full-scale treatment plant exposed to various concentrations of organotin wastewater. The organotin wastes were simulated by using analytical grade TBTO as an additive. Results of the Warburg tests served as guide to the TBTO loading of the continuousflow units. During the main period of this investigation, the continuous-flow units were operated under constant TBTO loading rates. Toward the end of the study the units were exposed to transient concentrations of TBTO in order to assess their response to such Ioadings. The operation and performance of the experimental treatment systems were evaluated by measuring conventional parameters such as organic and suspended solids concentration, and settling characteristics. Additionally, fish bioassay tests were conducted on raw wastewater and final effluent from the continuous-flow units to evaluate acute toxicity levels of the wastewaters. Continuous-flow tests

Three, 10-1. continuous-flow, biological reactors were used to evaluate the effects of continuous and transient organotin Ioadings on a biological waste treatment system.

Warburg evaluations

Warburg respirometer evaluations were used to set the organotin loads to reactors I and II. All Warburg flasks, except four control flasks (two thermobars and two seed blanks) were prepared to contain equivalent initial BODs:MLVSS ratios, based on 25.0 ml of solution in each flask. The procedure required that 15.0ml of sewage and 5.0 ml of mixed liquor be added to each test flask. Duplicate blanks (zero organotin) were diluted to a volume of 25.0 ml with distilled water while the duplicate flasks receiving organotin spikes were dosed based on the desired concentration in a final volume of 25.0 ml and the concentration of the TBTO stock solution. In this manner the only variable between the blank and the spiked flasks was the TBTO concentration. Substrate source

The organic substrate used throughout the study consisted of grab wastewater samples collected twice per week from a full-scale domestic wastewater treatment plant. The plant has no major industrial contributors and is not known to receive any wastewater containing organotin compounds. The sample was taken using a submersible pump placed downstream of an aerated grit chamber and upstream of a sludge return line. The sample point was chosen in order to minimize solids captured in the absence of primary clarifiers. The samples were collected in 55-gal drums and stored at 4~C until ready for use.

Organotin and activated sludge

537

C o m p l e t e - m i x biological reactor

Influent tank

E3 9

2 Air

[

w Effluent

Unit designation

Seed

Feed composition

Phase I - steady state C I II

Control Low orgonotin High orgonotin

"Domestic sewage Domestic sewage ÷organotin Domestic sewage + organotin

Unacclimated Acclimated Acclimated

Phase I I - transient load C

Control

Domestic sewage

Unacclimated

I

Test unit Control

Domestic sewage + organotin Domestic sewage + orgonotin

Unacclimated Acclimated

II

Fig. 1. Bench-scale continuous-flow activated sludge unit. The organotin spike in alt phases of the study was prepared weekly by diluting 100~ TBTO with distilled water to the desired concentration. The stock solution was monitored Monday to Friday for degradation and a new solution was prepared on Friday for use on the weekends. Preliminary tests indicated that very little TBTO degradation occurred at concentrations of 10.0-15.0 mg 1-*, but standard practice was to make up a new solution on Friday regardless of the concentration of the old solution.

Analytical schedule and methods The operation and performance of the three reactors were

monitored by periodic analyses of the standard parameters listed in Table 1. Microscopic examination of the sludges were periodically conducted. All analytical methods performed in this investigation conform to those outlined in APHA (1980). Performance monitoring tests such as zone settling velocity (ZSV) and specific oxygen uptake rate were conducted in accordance with commonly accepted procedures. Tin analyses of the stock solutions used in the study were performed according to Method 282.2 (Atomic Absorption, furnace technique) EPA (1979). Because no method for analyzing organotin compounds in domestic sewage was

Table 1. Activated sludge bench units, analytical schedule Analysis Type of sample Frequency lnfluent parameters BOD~, CODT TOC-r pH Effluent parameters BODT, COD-r, TOCr COD s, TOC s, TSS, VSS pH Aeration basin MLSS, MLVSS, ZSV, SVI, Oz-uptake pH, Temperature. DO *T = total; S = soluble.

Grab Grab Grab

2/week 3/week Daily

24h composite 24 h composite 24 h composite

l/week 3/week Daily

Grab Grab

3/week Daily

Y. ARGAMAN et al.

538

Table 2. Desired operating conditions of biological reactors C. 1 and I[ Parameter Value -lnrluent Flow rate 40 1day - d BOD unfiltered Variable Aeration basin Volume 10 t. Mixed liquor volatile suspended solids (M LVSS) 1800-2000 mg 1Hydraulic detention time 6h Temperature 20 :C Dissolved oxygen 2.0-4.0 mg I-

an independent laboratory confirmed the presence of an interfering matrix in municipal wastewaters in general rather than an interference specifically present in the stud,, wastewater. Simultaneously. 96-h static bioassays were conducted with treated and untreated wastewater. Treated effluent samples were obtained from the reactors operating with and without continuous TBTO additions. Untreated samples were obtained from spiked and un-spiked reactor influents. The purpose of the testing was to discern the difference in toxicity between the influent and effluent solutions to fathead minnows ( Pimephales promelas ).

REACTOR OPERATING CONDITIONS available at the time of the study, attempts were made to use the EPA technique on sewage samples spiked with known organotin concentrations. The inconsistency of the screening results indicated the presence of an interfering matrix in the sewage that prevented quantitative recovery of tin in the spiked samples. Analyses with this technique performed by

I

6

I

I

I

!

I

The desired operating conditions for all of the biological reactors are presented in Table 2. The influent value for unfiltered BOD varied due to the use of domestic wastewater as a feed source.

[

I

I

I

I

I

I

I

Z

{ T2BTO~do se/~-g;I ~ I

(i Unacclimated ,o.0 i

j

seed

50.0 / ,

IOO.O

,200.0 / '4 0 0 . 0 / / / / v / ~

Unocclimoted seed

~"200.O Seed occlimoted with 25.0 ,u.g I-~ TBTO dose

III

Seed occlimoted with 200.0 ,ag I-~ TBTO d o s e 0.0 IV ' 200.0 / 400~

/

~ / / / / / / / / / / / / / / / / / / / J Seed acclimated

with 1 0 0 0 . 0 Fg I-~ TBTO dose

,16000.0 ~

I lo

I

I

20

30

I 4o

I 50

I 6o

1 70

I 80

I 90

I lO0

I tlo

% 02 consumption Fig. 2. Summary of Warburg results at 96 h.

I 12o

I 13o

1 140

1.50

Organotin and activated sludge The remaining values represented controllable parameters for setting a baseline of specified operating conditions for the reactors. The food-to-microorganism ratio (F/M) fluctuated because of variations in influent concentration. The hydraulic retention time was held essentially constant and mixed liquor was wasted from the system to maintain the desired MLVSS range. COD (Chemical Oxygen Demand) and TOC (Total Organic Carbon) analyses were performed to eliminate the 5-day lag time associated with the BOD test and to serve as quality control checks on the degradation of the organic matter in the raw wastewater.

Continuous loading phase Throughout the continuous loading study, organotin was added to Unit I in the highest concentration at which no inhibitory effects were detected in the preceding Warburg evaluation. The spike to Unit II was based on the lowest concentration at which inhibitory effects were detected. The test reactors were operated at these loadings for a 2-week period at any given organotin concentration. During the second week of an operating cycle, a Warburg test was conducted using seed from Unit II at increased organotin doses. When the results of the Warburg were evaluated, organotin spikes to both test reactors were increased using the above criteria for dose determination. The sequence of Warburg evaluations, increased organotin Ioadings, and maintaining a one-cycle lag in organotin loading for Unit I was followed until the spike delivered to Unit II was at twice the estimated maximum loading.

Transient loading phase The transient loading tests were conducted at the completion of the continuous-flow study. The procedure followed in conducting the shock loading test was as follows: After reseeding and re-establishing continuous flow to Units C and I, all three reactors were fed raw sewage without an organotin spike for a period of three days. This allowed the reseeded units to stabilize and promoted the flushing of ambient organotin from the mixed liquor of Unit II. The test Units I and II were shocked with equivalent TBTO doses for a period of 2 days (eight hydraulic retention times) after which the feeding of raw sewage without organotin was resumed. All units were monitored for standard parameters during the respective shock and recovery periods. Five days after the first shock, Unit C and I were re-established and the sequence for conducting the shock test was repeated. Unit II was maintained as the acclimated seed control because it did not suffer a reduction in performance during the initial test.

539 RESULTS AND DISCUSSION

Warburg respirometer results The results of the Warburg Testing are summarized in Fig. 2. The results have been normalized relative to the seed blanks used in each test. This was accomplished by subtracting the oxygen consumption, measured for the duplicate seed blanks from the oxygen consumption measured in each of the duplicate control and test cultures. Percent oxygen consumption is reported relative to the control cultures on the premise that if increasing doses of TBTO added to the test cultures were toxic or inhibitory, oxygen consumption would be reduced relative to a control culture receiving no additional TBTO dose. Values for oxygen consumption in the test cultures which indicate a greater oxygen demand than the control are attributable to error with the respirometer equipment or an increase in biological activity due to the presence of low levels of TBTO. No method was available nor was any attempt made to determine the actual cause of this variation. The results of the Warburg tests indicate that unacclimated activated sludge cultures can be inhibited by TBTO at doses as low as 25.0#gl -~. However, the results also indicate that TBTO doses up to 8.0mg 1-~ can be tolerated with no inhibition when the cultures have been allowed to become acclimated. The course of acclimation can be followed in Fig. 2 when it is recognized that the seed used to make up the control and test cultures of Warburg experiments III, IV and V was taken from the high organotin continuous-flow reactor. Prior to each of these Warburg tests the high organotin culture had been exposed to continuous TBTO doses of respectively 25, 200 and 1000/~gl -~, as indicated in Fig. 2. In the Warburg experiment No. III, a sharp drop in oxygen consumption was seen as the TBTO dose increased from 100 to 200/~g l -~. Hence, it is concluded that the culture tolerance to TBTO in this test was between 100 and 200 #g 1-~. In experiment No. IV, there was no drop in oxygen consumption up to a TBTO dose of 500 ,ug 1-~ thus the tolerance level was greater than 500#gl -~. In experiment No. V, the tolerance level was between 8000 and 16,000 #g l -~ by virtue of the sharp drop in oxygen consumption that occurred as the TBTO dose was increased from 8000 to 16,000~gl -~. In each of these tests, the tolerance level was several times higher than the concentration to which the seed culture was acclimated. Since each of the Warburg tests was conducted within one week of increasing the organotin loading, the results appear to be indicative of rapid acclimation of the biomass.

Continuous organotin loading test results The continuous loading evaluations were conducted to determine the effects of organotin on the performance of an activated sludge treatment system.

Y. ARGAMANet al.

540

Table 3. Summary of average results continuous TBTO loading testing II Control Control I II Control 1 20{) 0 All units 0 12.5 25.0 0 100 Eff'luent averages Influent range 9 9 12 7 9 I1 la 72-108 4 3 5 3 2 2 5 45 63 53 45 51 51 83 216--280 28 32 43 36 26 36 42 I0 10 10 10 8 II IS 49-78 10 8 10 10 9 7 12 14 25 3t 7 13 9 9 100 Operatmg averages Operating range 3179 3504 3246 3030 2790 2600 2770 2300-3600 2516 2712 2589 2348 2228 2023 2099 1800-2700 4.0 3.8 4.6 4.3 4.8 4.0 5.1 3.0-6.5 0.26 0.26 0.25 0.24 0.22 0.23 0.23 0.15--0.30 21 21 21 21 21 21 2t 21 53 58 61 50 65 65 45 40-80 5.5 3.9 4.7 8.7 4.9 4.2 8.1 3.0-9.0 0.14 0,15 0.13 0.12 0.13 0.14 0.14 0.11-0.18 7.2 6.5 7.4 6.0 5.8 6.0 6.5 6-8

Unit TBTO dose {#g I-~) Water quality parameter BOD total (rag I-~) soluble (rag I-~) COD total (mg 1- ~) soluble (rag I -I) TOC total (rag I-~) soluble (rag I-~) TSS (mg I-~) Operational parameters MLSS (mg 1- B) MLVSS (rag I-I) DO (mg I-~) Oxygen uptake rate (g g- ~day-~) Temperature (~C) SVI (ml g-~) ZSV (m h -I) F/M (BOD) (gg-~day -~) Detention time (h)

The results o f this phase o f the study are presented in Tables 3 and 4. The effluent quality parameters summarized in Table 3 confirm the results predicted by the W a r b u r g testing. The acclimated biological cultures showed no reduction in p e r f o r m a n c e under any o f the increased loading conditions. N o significant degradation in effluent quality, as measured by effluent-organic levels or effluent suspended solids, was observed for dosages o f T B T O up to 1000,ug I-L This was the highest TBTO loading used in the testing and represents twice the m a x i m u m anticipated concentration in undiluted organotin wastewater from dry dock operations. M e a s u r e m e n t s o f parameters i m p o r t a n t to the operation o f the activated sludge system, specifically zone settling velocity and sludge volume index, indicated that activated sludge exposed to continuous T B T O loadings greater than or equal to 100,ugl -~ settled slower and thickened less readily than the control sludge. However, although the sludges exposed to T B T O exhibited poorer settling characteristics than the control sludge, the settling properties are considered excellent relative to sludges encountered in domestic wastewater treatment plants. Periodic microscopic examinations revealed the presence o f a great variety o f rotifers, stalked ciliates, and p r o t o z o a n s in the control unit sludge that were completely absent from units loaded with 100/.,g 1-~

I 500

lI 1000

17 4 66 37 I5 10 17

14 4 77 34 18 10 14

2355 1822 6.2 0.18 21 78 3.6 0.17 6.5

2513 1980 5.1 0.21 21 75 3.2 0.16 6.2

TBTO or higher. The test sludge populations appeared to be less diverse when compared to the control population. Operational and performance indicators derived from the data are presented in Table 4. The overall p e r f o r m a n c e indicators o f BOD and COD removals indicate no effect o f continuous TBTO loading up to 1000 p g 1-~. Other indicators, i.e. sludge volatile fraction, oxygen c o n s u m p t i o n , and sludge production show some variability but no consistent trend. This variability may be attributed to natural fluctuations in the short-term operating periods. Transient loading results

The transient or shock loading studies were conducted at the completion o f the continuous loading study in order to evaluate the effects o f transient organotin loads on acclimated and unacclimated biological systems. The results o f the testing are summarized in Table 5. The data of Table 5 indicate very little or no effect o f TBTO shock loading on the removal o f soluble organics at transient TBTO concentrations o f 500 and 1000,ttg I -I. The shock loading had an adverse effect on the sludge settling characteristics as reflected by the higher SVI and lower ZSV values in the test units compared to the control. The impaired settleability also resulted in higher effluent suspended solids and total organic concentrations. S o m e w h a t surprisingly, the un-

Table 4. Summary of derived parameters continuous TBTO loading testing Unit Control 1 lI Control I 11 TBTO dose (gl -*) 0 12.5 25.0 0 100 200 Parameter Sludge volatile fraction 67.8 77.4 79.8 77.5 79.9 77.6 BOD removed'l" 92 92 96 90 88 85 Yo BOD removed.}. + 97 97 97 96 98 97 Oxygen consumption gOzg BOD,"I.}.§ 1,88 1.82 1.94 2.04 1.67 1.66 Sludge production g VSS g BOD,"~ 0.44 0.70 0.68 0.86 0.78 0.65 *Based on or derived from average values. tBased on effluent total BOD. .}.Based on effluent soluble BOD. §g BOD, = g BOD removed.

Control 0 75.8 83 94 1.69 0.80

I 500

II 1000

77.4 80 95 1.13 0.52

78.8 83 95 1.39 0.72

Organotin and activated sludge

541

Table 5. Summary of average results transient TBTO loading testing Unit TBTO dose (g I-I)

Transient loading

Seed

Control 0

I 500

I1 500

Control 0

I I000

lI 1000

range of values Unacclimated Unacclimated Acclimated Unacclimated Unacclimated Acclimated

Water quality parameters

lnfluent range

BOD total (mgl -I)

Effluent averages

63-114

soluble (mg I-*) COD total (mg l -t) soluble (mg I -L) TOC total (mg 1-I) soluble (rag 1-*) TSS (mg 1-*) Operating parameters MLSS (rag I- *) MLVSS (rag l -t) DO (rag 1-I) Oxygen uptake rate (gg-i day-t) Temperature ("C) SVI (ml g-*) ZSV (m h -*) F/M (BOD) (gg-~day -~) Detention time (h)

5

7

100 Operatingrange 2200-3000 1800-2300 3.5-6.5 0.12-0.30

3 36 35 9 8 18

3 34 29 8 7 I1

2922 2218 3.8 0.30

19 50-81 2.9-5.8 0.10-0.25 6-7.5

19 54 5.8 0.18 6.2

179-438 33-51

acclimated systems appeared to be less affected by the shock loading c o m p a r e d to the acclimated system. Bioassay results Fish bioassay tests were performed to determine the 96-h LC~0 o f the influent a n d effluent, o f the c o n t i n u o u s load test units. T h e results o f the tests provided a measure o f the acute toxicity o f the influent and effluent wastewater a n d a qualitative d e t e r m i n a t i o n of the detoxification o b t a i n e d by biological treatment. The bioassay results are summarized in T a b l e 6. The data indicate a general increase in toxicity with increasing T B T O levels in the feed. In all cases, the toxicity of the wastewater was reduced by the activated sludge treatment. N o toxicity was observed in effluent samples with up to 100/~gl -~ T B T O in the influent. The influent wastewater with no T B T O also exhibited some toxicity which was removed in the t r e a t m e n t process. This toxicity was a t t r i b u t e d to constituents other t h a n T B T O c o n t a i n e d in the raw wastewater. It was estimated that 35% o f the observed toxicity was a t t r i b u t e d to n o n - T B T O sources. With this a s s u m p t i o n and the k n o w n T B T O concenTable 6. Summary of bioassay results 96-h LCso Values, % dilution TBTO

dose

95% confidence

(~zg I - *)

Sample description

Value

interval

0.0

lnfluent Effluent

73.9 T'I'L*

64.4-89.4 TTL

100

Influent Effluent

49.9 TTL

43.8-57.1 TTL

200

Influent Effluent

15.8 45.9

12.4-20.1 36.9-61.4

500

Influent Effluent

29.5 56.8

24.2-35.3 51.2-63.8

1000

lnfluent Effluent

7.1 21.7

4.6--10.8 4.6-25.2

*TTL--toxicity too low to calculate LCso.

W.R. 181~C

lI

8

2816 2140 5.8 0.18

2 2 45 23 39 22 9 9 9 7 27 4 Operating averages 2450 2893 1940 2214 5.1 4.6 0.21 0.19

19 63 4.2 0.19 6.2

19 73 3.1 0.22 6

19 69 4.8 0.tl 6

12

13

2 39 21 8 6 16

2 42

2523 1952 6.2 0.14

2279 1815 6.2 0.16

19 82 4.0 0.11 7.2

19 81 3.0 0.13 6.2

2t

13 7 17

trations in the feed wastewater, values of LCs0 expressed in ~ g 1-~ T B T O were calculated. The values thus calculated were 43, 67, 96 and 199 ~ g 1-~. These values are higher t h a n the previously reported LCs0 for bluegill o f 2 0 / l g l -t and 5 - 2 0 / ~ g l -~ for rainbow trout. T h e difference could be due to different test species, effect of other wastewater constituents, and loss o f T B T O by a d s o r p t i o n on reactor walls and tubing. CONCLUSIONS

U n a c c l i m a t e d activated sludge cultures can be inhibited by T B T O dosages as low as 2 5 # g l -~. However, T B T O doses greater t h a n 8 0 0 0 p g 1-~ can be tolerated by a well acclimated culture. The process o f acclimation appears to be rather rapid and the tolerance level is several times higher t h a n the T B T O c o n c e n t r a t i o n to which the culture was exposed during acclimation. C o n t i n u o u s T B T O loading of up to 1000 # g 1-~ had no effect on the overall performance o f bench-scale activated sludge systems as measured by effluent organic or suspended solids levels. Sludge settling a n d c o m p a c t i o n characteristics were adversely affected by T B T O dosages greater than or equal to 100 # g 1-~. Microscopic e x a m i n a t i o n showed m u c h less diversity in activated sludge systems exposed to T B T O c o m p a r e d to the control unit. T r a n s i e n t T B T O loadings o f 500 a n d 1000 ~ g I -~ had an insignificant effect on removal of soluble organics b o t h in acclimated and unacclimated activated sludge systems. The shock loadings had an adverse effect on sludge settling characteristics which also resulted in higher effluent suspended solids and total organic concentrations. Bioassay tests with fathead m i n n o w s indicated a T B T O 96-h LCs0 of 4 5 - 2 0 0 # g l -L. Toxicity was reduced considerably by the activated sludge treatment. Systems fed with 100/~g 1-~ T B T O or less had no toxicity in their effluent.

542

Y. ARGAMANet al. REFERENCES

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