Monitoring the toxicity of phenolic chemicals to activated sludge using a novel optical scanning respirometer.

This paper reports the development of optical scanning respirometer for determining the toxicity of chemicals to activated sludge. The respirometer is used to measure the dissolved oxygen concentration by monitoring the luminescence intensity of ruthenium dye immobilized in a polymer film in contact with the wastewater sample. The intensity is related to the extent of oxygen quenching of luminescence. The toxicity of chemicals can be evaluated by measuring the inhibition on respiration rate of microorganism using the scanning respirometer. The IC50 values (concentration of a chemical that exhibits 50% respiration inhibition) of various phenolic chemicals in activated sludge were determined. The performance of this method is compared with other toxicity methods. The experimental results indicate that the reproducibility and sensitivity of this respirometer are reasonably good.     

Fate of Terpene Compounds in Activated Sludge Wastewater Treatment Systems

ABSTRACT

Terpene-based cleaners are being widely used in industrial cleaning formulations because of their ability to replace suspected ozone-depleting chemicals such as 1,1,1-trichloroethane and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113). Substitution of chlorinated solvents with ter-pene-based cleaners, however, is expected to result in increased discharges to wastewater from industrial operations. A pilot-scale study was conducted at the U.S. Environmental Protection Agency's (EPA) Test & Evaluation Facility in Cincinnati, OH, to quantify the fate of specific terpene compounds in the activated sludge wastewater treatment process. Biodegradation rates of terpenes were estimated from the difference between the influent terpene mass flow rates and the amounts volatilized to air, partitioned to waste sludge, and passed through the treatment process unchanged. Any chemical transformation of the terpene compounds studied was attributed to biodegradation.

Analytical methods were developed to determine ter-pene concentrations in aqueous and gaseous media. The fate of two common terpene compounds (d-limonene and terpinolene) were evaluated in three identical pilot-scale systems: (1) a system with a high target spike range (2–10 mg/L), (2) a system with a low target spike range (0.5–2 mg/L), and (3) a control system (no spike).

The study showed that the primary removal mechanism for the terpene compounds in the activated sludge process is biodegradation. Typically, greater than 90% of the mass of terpenes entering the aeration basin of the activated sludge process biodegrades to other compounds; volatilization from the reaction basin accounts for less than 10%, while loss to waste activated sludge and the secondary clarifier effluent accounts for less than 1%.     

Environmental hazard profile of organic chemicals: An experimental method for the assessment of the behaviour of organic chemicals in the ecosphere by means of simple laboratory tests with 14C labelled chemicals

The concept of “Environmental Hazard Profile” developed at this institute has been tested with 100 ¹⁴C-labelled organic compounds. Concentration factors in activated sludge, in algae and fish were determined. The microbial degradation of the chemicals to CO₂ in activated sludge and the decomposition to CO₂ under artificial light were determined. Ranking of compounds is given in the order of falling concentration factors and accumulation in rats respectively, and decreasing rates of decomposition. Relationship between chemical structure and accumulative and degradative behaviours is demonstrated using some selected groups of chemicals, such as benzenes, phenols, biphenyls and polyaromatic hydrocarbons. Correlations between the octanol/water partition coefficient, concentration factors and rates of decomposition could be established. Evaluation of test compounds was possible using hazard profiles obtained by the sum of single test results.     

Determination of detoxification to Daphnia magna of four pharmaceuticals and seven surfactants by activated sludge

Pharmaceuticals are bioactive compounds generally resistant to biodegradation, which can make them problematic when they are released into nature. The use pattern for pharmaceuticals means that they are discharged into water via sewage treatment plants. Also surfactants are discharged through sewage treatment plants, primarily due to their use in detergents and shampoos and other cleaners. In this study the acute toxicity to Daphnia magna of four pharmaceuticals (ciprofloxacin, ibuprofen, paracetamol and zinc pyrithione) and seven surfactants (C8 alkyl glucoside, C6 alkyl glucoside, sodium caprylimidiopropionate, tallow-trimethyl-ammonium chloride, potassium decylphosphate, propylheptanol ethoxylate and alkylmonoethanolamide ethoxylate) was determined. Abiotic (without activated sludge bacteria) and biotic (with activated sludge bacteria) detoxification was also determined. The 24-h EC50s ranged from 2 μg L(-1) for the most toxic substance (zinc pyrithione) to 2 g L(-1) for the least toxic compound (C6 alkyl glucoside). Detoxification rates determined as the ratio between initial EC50 and EC50 after 1 week in water with activated sludge bacteria ranged from 0.4 (paracetamol) to 13 (zinc pyrithione). For most of these chemicals detoxification rate decreased after 1 week, but for one (alkylmonoethanolamide ethoxylate) it increased from about 2 to 30 times after 2 weeks. Many of these chemicals were "detoxified" also abiotically at about the same rate as biotically. Further studies are needed to determine the degradation products that were precipitated (aggregated) for some of the tested chemicals. Altogether, this study has shown that there are large differences in toxicity among chemicals entering sewage treatment plants, but also that the detoxification of them can differ. Therefore, the detoxification should receive more attention in the hazard and risk assessment of chemicals entering sewage treatment plants.     

Evaluation of the persistence of micropollutants through pure-oxygen activated sludge nitrification and denitrification.

The persistence of pharmaceuticals, hormones, and household and industrial chemicals through a pure-oxygen activated sludge, nitrification, denitrification wastewater treatment facility was evaluated. Of the 125 micropollutants that were tested in this study, 55 compounds were detected in the untreated wastewater, and 27 compounds were detected in the disinfected effluent. The persistent compounds included surfactants, fire-retardant chemicals, pesticides, fragrance compounds, hormones, and one pharmaceutical. Physical-chemical properties of micropollutants that affected partitioning onto wastewater solids included vapor pressure and octanol-water partition coefficients.     

Evaluation of the toxicity of substances to be assessed for biodegradability

The ability to distinguish between true non-biodegradability, and inhibition of biodegradability due to the toxic effects of the compound tested present problems. It results in possible false identification of substances as non-biodegradable.Six chemicals were evaluated in a variety of tests to assess their toxicity to aerobic sludge organisms. The tests employed were: BOD₅ and Closed Bottle inhibition tests, inhibition of respiration of activated sludge, growth inhibition of activated sludge, light emission from (MICROTOX test) and the repetitive die-away test (RDA). Results from these tests were compared with results obtained from a number of ready biodegradability tests using the compounds listed above at anticipated non-toxic and toxic concentrations.No test method evaluated consistently forecast toxicity due to the chemicals tested. The MICROTOX and nitrification inhibition tests were too sensitive. A combination of sludge respiration rate and/or growth tests seem most appropriate. To avoid toxicity to the sludge, biodegradability testing should be made at 10% of the EC₅₀ value. Compounds with an EC₅₀ value greater than 300 mg/l are unlikely to be toxic in ready biodegradability tests. Compounds with an EC₅₀ value of less than 20 mg/l may pose problems necessitating the use of the stringent closed bottle test, or the use of C¹⁴ labelled test materials. Compounds with an intermediate EC₅₀ that is between 20–300 mg/l, need to be evaluated at a range of concentrations in biodegradability tests, or may need to be evaluated carefully to define the precise no-effect level. Procedure recommendations to distinguish between the inhibition of biodegradability and inertness of the test substance are made.     

Co-treatment of acid mine drainage with municipal wastewater: performance evaluation

Co-treatment of acid mine drainage (AMD) with municipal wastewater (MWW) using the activated sludge process is a novel treatment technology offering potential savings over alternative systems in materials, proprietary chemicals and energy inputs. The impacts of AMD on laboratory-scale activated sludge units (plug-flow and sequencing batch reactors) treating synthetic MWW were investigated. Synthetic AMD containing Al, Cu, Fe, Mn, Pb, Zn and SO₄ at a range of concentrations and pH values was formulated to simulate three possible co-treatment processes, i.e., (1) adding raw AMD to the activated sludge aeration tank, (2) pre-treating AMD prior to adding to the aeration tank by mixing with digested sludge and (3) pre-treating AMD by mixing with screened MWW. Continuous AMD loading to the activated sludge reactors during co-treatment did not cause a significant decrease in chemical oxygen demand (COD), 5-day biochemical oxygen demand, or total organic carbon removal; average COD removal rates ranged from 87–93 %. Enhanced phosphate removal was observed in reactors loaded with Fe- and Al-rich AMD, with final effluent TP concentrations <2 mg/L. Removal rates for dissolved Al, Cu, Fe and Pb were 52–84 %, 47–61 %, 74–86 % and 100 %, respectively, in both systems. Manganese and Zn removal were strongly linked to acidity; removal from net-acidic AMD was <10 % for both metals, whereas removal from circum-neutral AMD averaged 93–95 % for Mn and 58–90 % for Zn. Pre-mixing with screened MWW was the best process option in terms of AMD neutralization and metal removal. However, significant MWW alkalinity was consumed, suggesting an alkali supplement may be necessary.     

Evaluation of a respirometric test method to determine the heterotrophic yield coefficient of activated sludge bacteria

The heterotrophic yield coefficient of activated sludge bacteria is an important parameter in the field of wastewater degradation kinetics and the determination of degradation kinetics of defined chemicals. With the help of easily biodegradable organic compounds like glucose and acetate the respiration kinetics of degrading activated sludge bacteria was studied. The results of the respiration analysis were transformed to examine the degradation and respiration kinetics of municipal wastewaters at different food to microorganism ratios (F/M ratios). It was proved that the heterotrophic yield coefficient of aerobically degrading activated sludge bacteria could reliably be determined and that the heterotrophic yield coefficient was independent of the F/M ratio over a wide range.     

A practical method for quantification of phosphorus- and glycogen-accumulating organism populations in activated sludge systems.

Enhanced biological phosphorus removal (EBPR) from wastewater relies on the enrichment of activated sludge with phosphorus-accumulating organisms (PAOs). The presence and proliferation of glycogen-accumulating organisms (GAOs), which compete for substrate with PAOs, may be detrimental for EBPR systems, leading to deterioration and, in extreme cases, failure of the process. Therefore, from both process evaluation and modeling perspectives, the estimation of PAO and GAO populations in activated sludge systems is a relevant issue. A simple method for the quantification of PAO and GAO population fractions in activated sludge systems is presented in this paper. To develop such a method, the activity observed in anaerobic batch tests executed with different PAO/GAO ratios, by mixing highly enriched PAO and GAO cultures, was studied. Strong correlations between PAO/GAO population ratios and biomass activity were observed (R2 > 0.97). This served as a basis for the proposal of a simple and practical method to quantify the PAO and GAO populations in activated sludge systems, based on commonly measured and reliable analytical parameters (i.e., mixed liquor suspended solids, acetate, and orthophosphate) without requiring molecular techniques. This method relies on the estimation of the total active biomass population under anaerobic conditions (PAO plus GAO populations), by measuring the maximum acetate uptake rate in the presence of excess acetate. Later, the PAO and GAO populations present in the activated sludge system can be estimated, by taking into account the PAO/GAO ratio calculated on the basis of the anaerobic phosphorus release-to-acetate consumed ratio. The proposed method was evaluated using activated sludge from municipal wastewater treatment plants. The results from the quantification performed following the proposed method were compared with direct population estimations carried out with fluorescence in situ hybridization analysis (determining Candidatus Accumulibacter Phosphatis as PAO and Candidatus Competibacter Phosphatis as GAO). The method showed to be potentially suitable to estimate the PAO and GAO populations regarding the total PAO-GAO biomass. It could be used, not only to evaluate the performance of EBPR systems, but also in the calibration of potential activated sludge mathematical models, regarding the PAO-GAO coexistence.     

Effect of textile auxiliaries on the biodegradation of dyehouse effluent in activated sludge

The textile industry is confronted with serious environmental problems associated with its immense wastewater discharge, substantial pollution load, extremely high salinity, and alkaline, heavily coloured effluent. Particular sources of recalcitrance and toxicity in dyehouse effluent are two frequently used textile auxiliaries; i.e. dye carriers and biocidal finishing agents. The present experimental work reports the observation of scientific and practical significance related with the effect of two commercially important textile dye carriers and two biocidal finishing agents on biological activated sludge treatment at a textile preparation, dyeing and finishing plant in Istanbul. Respirometric measurements of the dyehouse effluent spiked with the selected textile chemicals were carried out for the assessment of the "readily biodegradable COD fraction" of the wastewater. The respirometric data obtained to visualize the effect of the selected textile auxiliaries on biomass activity was evaluated by an adopted activated sludge model. Results have indicated that the tested biocides did not exert any significant inhibitory effect on the treatment performance of the activated sludge reactor at the concentrations usually encountered in the final, total dyehouse effluent. The situation with the dye carriers was inherently different; one dye carrier appeared to be highly toxic and caused serious inhibition of the microbial respirometric activity, whereas the other dye carrier, also known as the more ecological alternative, i.e. the "Eco-Carrier", appeared to be biodegradable. Finally, the respirometric profile obtained for the Eco-Carrier was described by a simplified respirometric model.     

Evaluation of laboratory-made sludge for an anaerobic biodegradability test and its use for assessment of 13 chemicals

Laboratory-made sludge for a biogas based anaerobic biodegradability test was prepared as an alternative for digested sludge from wastewater treatment plants (WWTPs). Biodegradation activities and background gas productions of digested sludge from various WWTPs were found to vary significantly depending on the source, which adversely affected test reliability. Subsequently, test conditions such as sludge concentration and sludge washing were examined with the laboratory-made sludge and a sludge concentration of 1.0 g-SS/L without washing was determined to be most suitable. Under these conditions, biodegradability tests were conducted for 13 select chemicals and their relative toxicities to methanogenic bacteria were evaluated. The results of biodegradability tests showed that chemicals with -OH and -CH2OH radicals were readily biodegraded and those with -Cl, -NO2, -NH2, -SO3H and -CH3 had inhibited degradation responses m-nitriphenol and 2,4,6-trichlorophenol were highly toxic to methanogenic bacteria, with m-nitrophenol completely inhibiting methane fermentation as low as 20 mg/L.     

The case for variable density: a new perspective on activated sludge settling.

A new, simple method for directly measuring activated sludge density was developed and applied, and the effects of biomass density on activated sludge settling in full-scale systems were evaluated. The driving force of sedimentation is the physical weight of the biological solids, but the role of biomass density in sedimentation has been largely ignored. Biomass density varied amongst treatment systems and this variability was correlated with settleability. Floc densities were approximately normally distributed within individual samples. Nonsoluble phosphorus content was a major contributor to density, and plants with enhanced biological phosphorus removal (EBPR) configurations generally had higher densities and better settleability than non-EBPR plants with similar filament contents. These results suggest that future work may benefit from consideration of density as a factor affecting activated sludge settling.     

Predicting diffuse-source transfers of surfactants to surface waters using SWAT

Chemicals present in domestic wastewater can adsorb to solid phase materials during sewage treatment. If biosolids (or sewage sludge) are applied to land, these chemicals can be transferred to soil. Under some circumstances they can also be transferred to surface waters during storm events either in solution or attached to sediment. In this paper we describe the utility of the SWAT 2000 model to estimate diffuse-source surface water exposure to "down-the-drain" chemicals. The model was applied hypothetically to predict the behaviour of linear alkylbenzene sulphonate (LAS), an anionic surfactant commonly used in household detergents, in a small catchment in Bedfordshire, UK, where it has previously been successfully validated for stream flow, sediments and pesticides. LAS transfers were estimated for two scenarios: (1) realistic and (2) reasonable worst case, based on assumptions on sludge application rates and the concentration of LAS in sludge. In addition, the sensitivity of the model output to the proportion of the catchment to which sludge is applied was established. Soil wetness and the total quantity of biosolids applied were the biggest determinants of chemical transport from the catchment. The potential of SWAT as a higher-tier tool in environmental risk assessments is discussed.     

蒽醌废水生化处理的活性污泥驯化

通过比较不同的污泥驯化方法研究了活性污泥法处理蒽醌废水的可行性.结果表明,常规的CODCr负荷提升法需要50 d才可以驯化出活性污泥.在进水中添加1 g/L葡萄糖可以快速提高污泥浓度,但是驯化出的污泥活性很低,不能满足废水的处理要求.最好的方法是添加1 g/L葡萄糖和原废水交叉循环驯化法,第28天就可以驯化出高活性的污泥.在平均进水CODCr为1 050 mg/L、HRT为24 h的条件下,CODCr去除率达到95.6%.     

Carbon dissipation from surgical cotton production wastewater using macroalgae,microalgae, and activated sludge microbes

Surgical cotton production has drastically been increased in the past few years due to excessive use by medical health professionals especially in countries like India, which is among the top three exporters of cotton worldwide. The effluent generated from surgical cotton industries differ from textile effluents by the conspicuous absence of dyeing chemicals. This wastewater has a high concentration of suspended particles, COD, dissolved ions, organic carbon, and alkaline pH. Several studies have been published on the treatment of textile effluents and the degradation of dyeing chemicals, while the treatment studies on surgical cotton wastewater have been rarely reported in spite of their potential to cause pollution in receiving land/water bodies. Activated sludge microbes have been extensively studied and well documented in the treatment of several industrial effluent but does not match to the production of valuable biomass from algae. The global energy demand has prompted the scientific community to investigate and explore the possibility of using algae for energy production with simultaneous wastewater treatment. To the best of the authors’ knowledge, no research articles have been published which compare the effectiveness of activated sludge microorganisms, microalgae, and macroalgae in removing contaminants from real wastewater. To date, there is a knowledge gap in understanding and selecting the right choice of biological system for effective and economical effluent treatment. In an attempt to minimize this gap, carbon removal by microalgae, macroalgae, and activated sludge microbes were investigated on real effluent from surgical cotton industries. It was observed that the strain of Chlorella vulgaris could dissipate 83% of COD from real wastewater, while consortia of macroalgae (consisting predominantly of Ulvaceae and Chaetomorpha) and activated sludge microbes could remove 81% and 69% of the carbon, respectively. The microalgal growth (in terms of wet weight) increased from 0.15 to 0.3 g, whereas the macroalgal wet weight increased from 1.5 to 3 g in over 7 days of batch experiments conducted in triplicates. This indicated the superlative performance of microalgae over activated sludge microbes in carbon dissipation.

     

Improved computational model (AQUIFAS) for activated sludge, integrated fixed-film activated sludge, and moving-bed biofilm reactor systems, part III: analysis and verification

Research was undertaken to analyze and verify a model that can be applied to activated sludge, integrated fixed-film activated sludge (IFAS), and moving-bed biofilm reactor (MBBR) systems. The model embeds a biofilm model into a multicell activated sludge model. The advantage of such a model is that it eliminates the need to run separate computations for a plant being retrofitted from activated sludge to IFAS or MBBR. The biofilm flux rates for organics, nutrients, and biomass can be computed by two methods-a semi-empirical model of the biofilm that is relatively simpler, or a diffusional model of the biofilm that is computationally intensive. Biofilm support media can be incorporated to the anoxic and aerobic cells, but not the anaerobic cells. The model can be run for steady-state and dynamic simulations. The model was able to predict the changes in nitrification and denitrification at both pilot- and full-scale facilities. The semi-empirical and diffusional models of the biofilm were both used to evaluate the biofilm flux rates for media at different locations. The biofilm diffusional model was used to compute the biofilm thickness and growth, substrate concentrations, volatile suspended solids (VSS) concentration, and fraction of nitrifiers in each layer inside the biofilm. Following calibration, both models provided similar effluent results for reactor mixed liquor VSS and mixed liquor suspended solids and for the effluent organics, nitrogen forms, and phosphorus concentrations. While the semi-empirical model was quicker to run, the diffusional model provided additional information on biofilm thickness, quantity of growth in the biofilm, and substrate profiles inside the biofilm.     

Toxicity of metals and organic chemicals evaluated with bioluminescence assays

The development of a bioluminescent sensor organism (Shk1) that was created for assessing wastewater toxicity was reported several years ago. In order to establish a test battery to better characterize wastewater toxicity, additional luminescent sensor organisms were later created. The present study focused on one promising candidate (PM6), a Pseudomonas spp. strain, because of its high level of luminescence compared to that of other newly created organisms. Using a batch toxicity testing protocol, the toxicity of 7 metals and 25 organic compounds was evaluated with the PM6 and Shk1 assays. Results indicated that the toxicity data of the PM6 and the Shk1 assays were correlated, and no assay appeared to be particularly more sensitive to a group of toxicants than the other assay. The results of the PM6 and Shk1 assays were further evaluated by comparing with the results of the Vibrio fischeri luminescence inhibition assay and activated sludge inhibition assays. Data suggested that PM6 and Shk1 more closely represented activated sludge organisms than V. fischeri. The suitability of using PM6 and Shk1 for assessing wastewater toxicity on activated sludge, both individually and in a test battery, was discussed.     

Improved computational model (AQUIFAS) for activated sludge, integrated fixed-film activated sludge, and moving-bed biofilm reactor systems, Part I: Semi-empirical model development

Research was undertaken to develop a model for activated sludge, integrated fixed-film activated sludge (IFAS), and moving-bed biofilm reactor (MBBR) systems. The model can operate with up to 12 cells (reactors) in series, with biofilm media incorporated to one or more cells, except the anaerobic cells. The process configuration can be any combination of anaerobic, anoxic, aerobic, post-anoxic with or without supplemental carbon, and reaeration; it can also include any combination of step feed and recycles, including recycles for mixed liquor, return activated sludge, nitrates, and membrane bioreactors. This paper presents the structure of the model. The model embeds a biofilm model into a multicell activated sludge model. The biofilm flux rates for organics, nutrients, and biomass can be computed by two methods--a semi-empirical model of the biofilm that is relatively simpler, or a diffusional model that is computationally intensive. The values of the kinetic parameters for the model were measured using pilot-scale activated sludge, IFAS, and MBBR systems. For the semiempirical version, a series of Monod equations were developed for chemical oxygen demand, ammonium-nitrogen, and oxidized-nitrogen fluxes to the biofilm. Within the equations, a second Monod expression is used to simulate the effect of changes in biofilm thickness and fraction nitrifiers in the biofilm. The biofilm flux model is then linked to the activated sludge model. The diffusional model and the verification of the models are presented in subsequent papers (Sen and Randall, 2008a, 2008b). The model can be used to quantify the amount of media and surface area required to achieve nitrification, identify the best locations for the media, and optimize the dissolved oxygen levels and nitrate recycle rates. Some of the advanced features include the ability to apply different media types and fill fractions in cells; quantify nitrification, denitrification, and biomass production in the biofilm and mixed liquor suspended solids; and perform dynamic simulations.     

The need for applying stability tests in biodegradability assessments

Out of fourteen chemicals tested, two - hexamethylenetetramine and sodium benzene sulphinate - were degraded in screening tests (>70% DOC removal, >60% ThOD exerted) but not in activated sludge simulation tests (<25% DOC removal). It is suggested from data in the literature that these essentially non-biodegradable chemicals undergo hydrolysis or autoxidation in the 28-day screening tests to form biodegradable products, which are not produced in sufficient quantity in the 3-hour simulation test. The need is stressed for taking account of the stability of chemicals in water when assessing biodegradability in the environment.     

Competition between polyphosphate- and glycogen-accumulating organisms in enhanced-biological-phosphorus-removal systems: effect of temperature and sludge age.

Temperature and sludge age were found to be important factors in determining the outcome of competition between polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating non-polyphosphate organisms (GAOs) and the resultant stability of enhanced-biological-phosphorus removal (EBPR). At 20 degrees C and a 10-day sludge age, PAOs were dominant in an anaerobic/aerobic (A/O) sequencing-batch reactor (SBR), as a result of their higher anaerobic-acetate-uptake rate and aerobic-biomass yield than GAOs. However, at 30 degrees C and a 10-day sludge age, GAOs were able to outcompete PAOs in the A/O SBR because of their higher anaerobic-acetate-uptake rate than PAOs. At 30 degrees C and a 5-day sludge age, GAOs coexisted with PAOs in the A/O SBR, resulting in unstable EBPR performance. At 30 degrees C, reducing the sludge age from 5 to 3 days improved the EBPR efficiency drastically, and the EBPR performance was stable. The maximum specific-anaerobic-acetate-uptake rates of GAO-enriched sludge were affected by temperature with the Arrhenius temperature coefficient theta of 0.042 (degrees C(-1) between 10 and 30 degrees C. The effect of sludge age (5 and 10 days) on the maximum specific-anaerobic-acetate-uptake rates of GAO-enriched activated sludge, however, was not significant. For the PAO-enriched activated sludge, the maximum specific-anaerobic-acetate-uptake rate did not change significantly between 20 and 30 degrees C, but significantly increased from 0.38 to 0.52 mmol-C/ mmol-C/h as the sludge age decreased from 10 to 3 days at 30 degrees C.