Activated Sludge Treatment System Research Articles

Potential of a bacterial consortium to degrade azo dye Disperse Red 1 in a pilot scale anaerobic–aerobic reactor

The textile industry is the largest consumer of azo dyes and activated sludge treatment systems typically used to remove them are frequently inefficient, resulting in significant quantities of these compounds adsorbed in the sludge or released into water bodies. The aim of this study was to evaluate the biodegradation of the commercial azo dye Disperse Red 1 in a pilot scale anaerobic–aerobic reactor inoculated by a microbial consortium selected for its capacity to degrade azo dyes. Dye decolorization (80%) occurred in 60h in the anaerobic reactor and 92% COD (chemical oxygen demand) was removed as measured in the treated effluent. LC–ESI-MS/MS of the treated effluent showed the formation of a reduced azo bond and azo bond cleavage and subsequent degradation products. Aromatic amines produced by the cleavage of the azo bond were not detected. Toxicity tests performed with Daphnia similis and Hydra attenuata in the treated effluent showed that the toxicity was reduced significantly. Mutagenicity, evaluated using the Salmonella/microsome Ames test, found the untreated dye medium was only mutagenic toward Salmonella strain YG1041. However after treatment, only marginal mutagenicity was observed. These results indicate the bacterial consortium was effective in biodegrading Disperse Red 1 and also reducing the toxicity and mutagenicity and may represent a promising application for dyes biodegradation.

Effect of short-term exposure of selected aromatic nitrogen compounds on wastewater treatment.

The biodegradation of melamine and p-nitrophenol (PNP) and their impact on wastewater treatment was evaluated after a short-term individual chemical loading in activated sludge treatment systems. Melamine was not degraded and quickly washed out of the system. PNP was degraded, but it led to a prolonged period of nitrification inhibition and deterioration of effluent quality. Both melamine and PNP loadings increased the effluent nitrogen concentrations, with their main contributors being melamine and NH4+, respectively. Nitrosomonas and Nitrospira were dominant in the activated sludge. Melamine did not affect the nitrifying assemblages, whereas PNP led to a reduced Nitrosomonas population size and complete washout of Nitrobacter. The results suggest that melamine is an inert compound if it enters the treatment facility for a short duration. Although the short-term exposure of melamine or PNP decreased effluent water quality,the impact of such aromatic nitrogen compounds on wastewater treatment performance may vary significantly. Water

Real scale environmental monitoring of zoonotic protozoa and helminth eggs in biosolid samples in Brazil.

Biosolid is the product of the activated sludge treatment system and its final disposition is subject of ongoing discussion as this residue can therefore harbor a great number and variety of pathogens. This study was aimed to (1) monitor the presence of Giardia and Cryptosporidium in biosolid samples from a treatment plant in Campinas, SP, Brazil, (2) observe Giardia cyst wall morphological integrity in treated samples using scanning electron microscopy (SEM) and (3) verify the presence and viability of helminth eggs. Cysts were present in 33.3% of the samples, whereas oocysts were detected in 8.3%. Viable Ascaris sp. Toxocara sp. and similar to Trichuris sp. eggs were found through the use of Mexican Official Norm. Results demonstrate the difficulties inherent in working with biosolid as factors such as temperature, ionic strength and pH influenced the recovery of cysts and oocysts. Pores and ruptures were not observed in cyst wall visualized by SEM following 45days of exposure to sunlight, only minimal morphological changes. These observations emphasize both the importance of adequate treatment of sewage sludge and the need to develop appropriate techniques for the detection of Giardia and Cryptosporidium in this type of sample. This is the first time that a study was done in a real scale for biosolid samples in determining the presence of pathogenic protozoa as Giardia and Cryptosporidium in Brazil, and also observed minimal cyst wall damage after sunlight treatment.

Characterization of cefalexin degradation capabilities of two Pseudomonas strains isolated from activated sludge

Pharmaceuticals have recently been regarded as contaminants of emerging concern. To date, there is limited knowledge about antibiotic-degrading microorganisms in conventional activated sludge treatment systems and their characteristics toward antibiotic degradation especially in the presence of a pharmaceutical mixture. As such, antibiotic-degrading microorganisms were investigated and isolated from the activated sludge, and their degradation capabilities were evaluated. Two strains of cefalexin-degrading bacteria CE21 and CE22 were isolated and identified as Pseudomonas sp. in the collected activated sludge. Strain CE22 was able to degrade over 90% of cefalexin, while CE21 was able to remove 46.7% of cefalexin after incubation for 24h. The removal efficiency of cefalexin by CE22, different from that of CE21, was not significantly affected by an increase in cefalexin concentration, even up to 10ppm, however the presence of 1ppm of other pharmaceuticals had a significant effect on the degradation of cefalexin by CE22, but no significant effect on CE21. The degradation product of cefalexin by the two strains was identified to be 2-hydroxy-3-phenyl pyrazine. Our results also indicated that CE21 and CE22 were able to degrade caffeine, salicylic acid and chloramphenicol. Moreover, CE21 was found to be capable of eliminating sulfamethoxazole and naproxen.

Ecophysiology of nitrifying communities in membrane bioreactors

Membrane bioreactors (MBRs) are rapidly becoming the technology of choice over conventional activated sludge treatment systems due to their smaller footprint, reduced sludge production, rapid start-up of biological processes, complete removal of suspended solids and better effluent quality. The retention of sufficient amount of slow-growing nitrifiers makes it feasible for the MBRs to achieve strong tolerance against the shock loads with stable and highly efficient nitrogen removal. Various studies have focused on the ecophysiology of nitrifiers in MBRs as well as their distinctive operational parameters as well as their impact on the selection and activity of nitrifying community. Several techniques have been employed over the years to understand the nitrifying community and their interaction within the MBR system, which led to its modification from the initial design. This review focuses on the identification of optimal operational and environmental conditions for efficient nitrification in MBRs. The advantages and limitations of different techniques employed for investigating the nitrifying communities in MBRs are also emphasized.

Removal of endocrine-disrupting chemicals and conventional pollutants in a continuous-operating activated sludge process integrated with ozonation for excess sludge reduction

Sludge ozonation is considered as a promising technology to achieve a complete reduction of excess sludge, but as yet its effects on the removal of endocrine-disrupting chemicals (EDCs) and conventional pollutants (i.e., COD, N and P) in the activated sludge process are still unclear. In this study, two lab-scale continuous-operating activated sludge treatment systems were established: one was operated in conjunction with ozonation for excess sludge reduction, and the other was operated under normal conditions as control. The results indicate that an ozone dose of 100mgO3g−1SS led to a zero yield of excess sludge in the sludge-reduction system during a continuous-operating period of 45d. Although ozonation gave a relatively lower specific oxygen uptake rate of activated sludge, it had little effect on the system’s removal performance of COD and nitrogen substances. As a plus, sludge ozonation contributed a little more removal of target EDCs (estrone, 17β-estrodiol, estriol, 17α-ethinylestradiol, bisphenol A, and 4-nonylphenol). However, the total phosphorus removal declined notably due to its accumulation in the sludge-reduction system, which necessitates phosphorus recovery for the activated sludge process.

Filamentous sludge bulking control by nano zero-valent iron in activated sludge treatment systems.

Sludge bulking causes loss of biomass in the effluent and deterioration of effluent water quality. This study explored the use of nano zero-valent iron (NZVI with an average particle size of 55 ± 11 nm) for sludge bulking control. In two Modified Ludzack-Ettinger (MLE) activated sludge treatment systems, a single dose of NZVI at the final concentration of 100 mg Fe per L in the mixed liquor reduced the number of filamentous bacteria Type 021N by 2-3 log units (a reduction of 99.9 and 96.7% in MLE tank #1 and #2, respectively). The side effect of the use of NZVI depended on sludge bulking conditions and biomass concentration. In the system with sludge bulking and significant sludge loss (average biomass concentration of 1022 ± 159 COD mg per L or at the ratio of 0.098 g Fe per g biomass COD), the use of NZVI increased effluent COD, NH4(+)-N and NO2(-)-N concentrations, as also evident with the loss of nitrifying populations and nitrifying activities resulting in more than 40 days to have the full recovery of the activated sludge system. In contrast, in the system with the early stages of bulking and the biomass concentration of 1799 ± 113 COD mg per L (at the ratio of 0.056 g Fe per g biomass COD), the effluent water quality and overall bioreactor performance were only slightly affected for a few days.

Fractionation of wastewater characteristics for modelling of Firle Sewage Treatment Works, Harare, Zimbabwe

Varying conditions are required for different species of microorganisms for the complex biological processes taking place within the activated sludge treatment system. It is against the requirement to manage this complex dynamic system that computer simulators were developed to aid in optimising activated sludge treatment processes. These computer simulators require calibration with quality data input that include wastewater fractionation among others. Thus, this research fractionated raw sewage, at Firle Sewage Treatment Works (STW), for calibration of the BioWin simulation model. Firle STW is a 3-stage activated sludge system. Wastewater characteristics of importance for activated sludge process design can be grouped into carbonaceous, nitrogenous and phosphorus compounds. Division of the substrates and compounds into their constituent fractions is called fractionation and is a valuable tool for process assessment. Fractionation can be carried out using bioassay methods or much simpler physico-chemical methods. The bioassay methods require considerable experience with experimental activated sludge systems and associated measurement techniques while the physico-chemical methods are straight forward. Plant raw wastewater fractionation was carried out through two 14-day campaign periods, the first being from 3 to 16 July 2013 and the second was from 1 to 14 October 2013. According to the Zimbabwean Environmental Management Act, and based on the sensitivity of its catchment, Firle STW effluent discharge regulatory standards in mg/L are COD (<60), TN (<10), ammonia (<0.2), and TP (<1). On the other hand Firle STW Unit 4 effluent quality results based on City of Harare records in mg/L during the period of study were COD (90±35), TN (9.0±3.0), ammonia (0.2±0.4) and TP (3.0±1.0). The raw sewage parameter concentrations measured during the study in mg/L and fractions for raw sewage respectively were as follows total COD (680±37), slowly biodegradable COD (456±23), (0.7), readily biodegradable COD (131±11), (0.2), soluble unbiodegradable COD (40±3), (0.06), particulate unbiodegradable COD (53±3) (0.08), total TKN (40±4) mg/L, ammonia (28±6), (0.68), organically bound nitrogen (12±2), (0.32), TP (15±1.4), orthophosphates (9.6±1.4), (0.64), and organically bound TP (5.4±1.4), (0.36), soluble unbiodegradable TP (0.4±0), (0.03), particulate unbiodegradable TP (0.05±0), (0.003). Thus, wastewater at Firle STW was found to be highly biodegradable suggesting optimisation of biological nutrient removal process will generally achieve effluent regulatory standards compliance. Thus, opportunities for plant optimisation do exist of which modelling with the use of a simulator is recommended to achieve recommended effluent standards in addition to reduction of operating costs.

Effect of magnetic nanoparticles on the performance of activated sludge treatment system

Both short-term and long-term exposure experiments were carried out to investigate the influence of magnetic nanoparticles (NPs) on activated sludge. The short-term presence of 50-200 mg/L of NPs decreased total nitrogen (TN) removal efficiencies, resulted from the acute toxicity of a shock load of NPs. However, long-term exposure of 50 mg/L magnetic NPs were observed to significantly improve TN removal efficiency, partially due to the self-repair function of activated sludge and magnetic-induced bio-effect. Sludge properties and extracellular polymer substrates secretion were affected. Additional investigations with enzyme and FISH assays indicated that short-term exposure of 50 mg/L magnetic NPs led to the abatement of nitrifying bacteria. However, the activities of the enzyme nitrite oxidoreductase and key denitrifying enzymes were increased after long-term exposure.

Life cycle assessment of small-scale constructed wetland and extended aeration activated sludge wastewater treatment system

Wastewater treatment plants help to reduce negative impact on the environment by improving the quality of effluent. Different technologies are used in wastewater treatment, and one of the tasks is to find the most environmentally sound option, taking into account the use of resources and energy during construction and operation of the treatment system. The aim of the study is to assess environmental impacts from two different types of small-scale wastewater treatment systems, a constructed wetland and extended aeration activated sludge treatment system using Life Cycle Assessment method. The system boundaries include construction and operation phases. Assessment has been carried out using SimaPro software and Impact 2002? and ReCiPe assessment methods with characterisation and normalisation stages. The results show that the main negative impact of constructed wetland is caused by the construction phase and use of lightweight expanded clay aggregate to construct the hybrid filter. Impacts from extended aeration activated sludge treatment system are mainly caused from the use of electricity and the quality of the effluent, therefore, the use phase has a larger impact on the life cycle. Since a large amount of energy is used to produce lightweight expanded clay aggregate, the impact of 1 population equivalent of con- structed wetland is larger than the impact of extended aeration activated sludge treatment system. Constructed wetland dominates in human toxicity, acidification, land use, ozone layer depletion and the use of non-renewable resources categories. Extended aeration activated sludge treatment system dominates in categories associated with eutrophication and ecotoxicity.

Fate and toxicity of melamine in activated sludge treatment systems after a long-term sludge adaptation

Melamine is a nitrogen-rich (67% nitrogen by mass) heterocyclic aromatic compound that could significantly increase effluent total nitrogen concentrations. In this study, we investigated the degradation of melamine and its impact on activated sludge operations by employing two common activated sludge processes, namely the Modified Ludzack-Ettinger (MLE) process and the continuous stirred tank reactor (CSTR) process. Melamine was dosed continuously from day 125 in both activated sludge treatment systems at an influent concentration of 3 mg/L for about 100 days. Even after such a long period of sludge adaptation, melamine appeared not to be easily biodegradable. The average melamine removal efficiencies in the CSTR and MLE systems were 14 ± 10% and 20 ± 15%, respectively. There was no significant difference in melamine removal between the two different activated sludge processes. The long-term input of melamine resulted in a decrease in the nitrifying bacterial activities (by 82 ± 8%) and population in both systems. Short-term microtiter assay results also showed that melamine reduced activated sludge growth by 80% when supplied at a concentration of 75.6 mg/L. These results suggest that sludge adaptation plays a minimal role in melamine degradation, as the enzymes responsible for hydrolytic deamination of melamine in activated sludge are not easily induced. The insignificant biodegradation of melamine is also attributed to bacterial growth inhibition under long-term dosing conditions with melamine, resulting in a significant decrease in effluent water quality.

Genome-scale metabolic modeling to provide insight into the production of storage compounds during feast–famine cycles of activated sludge

Studying storage metabolism during feast-famine cycles of activated sludge treatment systems provides profound insight in terms of both operational issues (e.g., foaming and bulking) and process optimization for the production of value added by-products (e.g., bioplastics). We examined the storage metabolism (including poly-β-hydroxybutyrate [PHB], glycogen, and triacylglycerols [TAGs]) during feast-famine cycles using two genome-scale metabolic models: Rhodococcus jostii RHA1 (iMT1174) and Escherichia coli K-12 (iAF1260) for growth on glucose, acetate, and succinate. The goal was to develop the proper objective function (OF) for the prediction of the main storage compound produced in activated sludge for given feast-famine cycle conditions. For the flux balance analysis, combinations of three OFs were tested. For all of them, the main OF was to maximize growth rates. Two additional sub-OFs were used: (1) minimization of biochemical fluxes, and (2) minimization of metabolic adjustments (MoMA) between the feast and famine periods. All (sub-)OFs predicted identical substrate-storage associations for the feast-famine growth of the above-mentioned metabolic models on a given substrate when glucose and acetate were set as sole carbon sources (i.e., glucose-glycogen and acetate-PHB), in agreement with experimental observations. However, in the case of succinate as substrate, the predictions depended on the network structure of the metabolic models such that the E. coli model predicted glycogen accumulation and the R. jostii model predicted PHB accumulation. While the accumulation of both PHB and glycogen was observed experimentally, PHB showed higher dynamics during an activated sludge feast-famine growth cycle with succinate as substrate. These results suggest that new modeling insights between metabolic predictions and population ecology will be necessary to properly predict metabolisms likely to emerge within the niches of activated sludge communities. Nonetheless, we believe that the development of this approach will help guide the optimization of the production of storage compounds as valuable by-products of wastewater treatment.

Optimization and/or acclimatization of activated sludge process under heavy metals stress

The present study aimed to overcome the toxicity of the heavy metals load, discharged with the industrial effluents into Alexandria sewerage network, on the activated sludge treatment system through effective acclimation for organic matter and heavy metals removal. Optimization and/or acclimatization of the activated sludge process in the presence of Cu, Cd, Co and Cr contaminating mixed domestic-industrial wastewater was investigated. Acclimatization process was performed through abrupt and stepwise addition of tested metals using sequencing batch reactors treatment approach and evaluated as microbial oxygen uptake rate (OUR), dehydrogenase activity (DHA), organic matter (COD) and heavy metals removal. Abrupt addition of metals adversely affected sludge bioactivity leading to decline in the removal efficiency of the targeted contaminants and loss of floc structure. Metals IC50 confirmed that copper possessed the highest toxicity towards the OUR, DHA activity and COD removal with orders Cu > Cd > Cr > Co; Cu > Cd > Co = Cr and Cu > Cd > Cr > Co, respectively. The highest metal removal was recorded for Cd followed by Co, Cu and finally Cr, most of which was retained in the dissolved influent. However, controlled stepwise application of the tested metals exhibited high sensitivity of DHA and OUR activities only at the highest metal concentrations although enhanced at the lowest concentrations while COD removal was not significantly affected. In conclusion, this approach resulted in adaptation of the system where sludge microbes acquired and developed natural resistance to such metals leading to remarkable enhancement of both organic matter and heavy metals removal.

Comparison of Activated Sludge Technologies by Particle Size Analysis

This paper analyses the influence of activated sludge technologies on the Particle Size Distribution (PSD) of urban wastewater treatment plants operating under real conditions. The activated sludge treatment systems selected for the analysis are the most widely used in wastewater treatment installations: (a) double step activated sludge, (b) medium load activated sludge, (c) prolonged aeration, and (d) membrane bioreactors The main quality parameters (suspended solids, turbidity, and COD) and PSD in the influent and effluent of each different activated sludge treatment were analyzed during 1 year. The PSD was fitted using the power law ( $$ n\left( {{d_{\text{P}}}} \right) = \frac{{\partial {\text{N}}\left( {{d_{\text{p}}}} \right)}}{{\partial {d_{\text{p}}}}} = A \cdot d_{\text{p}}^{{ - b \cdot {\text{Log}}\left( {{d_{\text{p}}}} \right)}} $$ ) obtaining coefficients A and b to define the particle distribution. Mathematical correlations between this coefficients and the rest of parameters studied were found $$ \left( {\matrix{ {{\text{SS}} = {0}{.0126} \cdot {A^{{{0}{.781}}}},} &{{\text{Turbidity}} = 15.5814 + 1.164 \cdot {{10}^3} \cdot A{,}} &{{\text{COD}} = \frac{{1}}{{{0}{.0133} + \cdot \frac{{{49}{.85}}}{\text{A}}}}} \\ } } \right) $$ . The relation with the average particle size by mass was also found, ( $$ {d_{\text{pma}}} = - 11.6502 + \frac{{50.4265}}{b} $$ ). Moreover, a relation between PSD and the particle elimination efficiency of the secondary treatment was study, ( $$ \eta = 0.1434 - \frac{{0.5602}}{{{A_{\text{rel}}}}} + \frac{{0.7490}}{{{b_{\text{rel}}}}} $$ ). Finally, the particulate matter nature was assessed by SEM-EDX. It can be concluded that membrane bioreactor is the technology that produces the best water quality effluent due to physic process of particle separation by ultrafiltration membrane technology.

Production of α-amylase by Aspergillus oryzae from cassava bagasse and wastewater sludge under solid-state fermentation

The potential of cassava bagasse (from cassava starch production) and biological sludge (biosludge, from an activated sludge treatment system) was investigated for α-amylase production using Aspergillus oryzae TISTR 3605 under solid-state fermentation and the optimum conditions for enzyme production were determined. The optimum conditions for α-amylase production were 48 h of incubation, using a ratio of cassava bagasse and biosludge of 3:2 (w/w) at a moisture content of 60%, with 1 mL inoculum and distilled water as the moisturizing agent. The influence of supplementation with carbon sources (glucose and starch) suggested that only glucose increased α-amylase production and then slightly. However, supplementing with nitrogen sources (peptone and ammonium sulfate) had no positive effect on amylase production. The results suggested that cassava bagasse and wastewater sludge had potential to be used as carbon and nutrient sources, respectively, for microorganisms to produce α-amylase. However, further study is needed to improve the α-amylase yield. © 2011 American Institute of Chemical Engineers Environ Prog, 2012

Prediction of activated sludge filamentous bulking using ATP data and neural networks

AbstractNeural networks (NNs) were used to predict the onset of filamentous bulking, as described by trends in stirred sludge volume index, in a pulp and paper activated sludge treatment system. Variables related to activated sludge biomass viability, namely specific oxygen uptake rate (SOUR) and adenosine triphosphate (ATP), were used as inputs to the NN. ATP data were shown to improve NN performance in providing an early warning signal for bulking, both in terms of accuracy and prediction delay. A warning signal system was developed to provide operators with enough time to react and further investigate the causes of bulking.

Bacterial response to a shock load of nanosilver in an activated sludge treatment system

The growing release of nanosilver into sewage systems has increased the concerns on the potential adverse impacts of silver nanoparticles (AgNPs) in wastewater treatment plants. The inhibitory effects of nanosilver on wastewater treatment and the response of activated sludge bacteria to the shock loading of AgNPs were evaluated in a Modified Ludzack–Ettinger (MLE) activated sludge treatment system. Before shock-loading experiments, batch extant respirometric assays determined that at 1 mg/L of total Ag, nitrification inhibitions by AgNPs (average size = 1–29 nm) and Ag + ions were 41.4% and 13.5%, respectively, indicating that nanosilver was more toxic to nitrifying bacteria in activated sludge than silver ions. After a 12-h period of nanosilver shock loading to reach a final peak silver concentration of 0.75 mg/L in the MLE system, the total silver concentration in the mixed liquor decreased exponentially. A continuous flow-through model predicted that the silver in the activated sludge system would be washed out 25 days after the shock loading. Meanwhile, a prolonged period of nitrification inhibition (>1 month, the highest degree of inhibition = 46.5%) and increase of ammonia/nitrite concentration in wastewater effluent were observed. However, nanosilver exposure did not affect the growth of heterotrophs responsible for organic matter removal. Microbial community structure analysis indicated that the ammonium-oxidizing bacteria and nitrite-oxidizing bacteria, Nitrospira, had experienced population decrease while Nitrobacter was washed out after the shock loading.

Performance evaluation of biosimulator for treating domestic wastewater using activated sludge treatment system

This research investigation was aimed at demonstrating the performance evaluation of pilot activated sludge treatment system (biosimulator; model MF-114). An intensive analytical program was followed for evaluating the performance efficiency of the biosimulator by maintaining the dissolved oxygen (DO) concentration at 4.0 mg/L throughout the study period. Biosimulator performance was evaluated after every 2 hours and analyzed for pH, DO, COD, ammonia-nitrogen (NH3-N), nitrite-nitrogen (NO2-N) and nitrate-nitrogen (NO3-N). In all ten experimental replicates were performed and the mean figures are taken for discussion. Although no significant variation in the pH was observed during the study period but the mean pH values of the samples during the treatment process gradually increased and it ranged from 6.81-7.52. The removal of COD was found to be in direct relationship with retention time and the mean COD of the raw wastewater samples ranged from 164-1160 mg/L whereas it gotreduced considerably during the treatment process and the mean removal efficiency was found to be 86%. The COD and NO2-N removal efficiency was better than NH3-N and NO3-N this is considered to be satisfactory especially with respect to organic loading and retention time. Similarly, the mean NH3-N values of wastewater after 29 hours oftreatment were found to be fluctuating between 14.52-20.54 mg/L whereas the mean NO3-N level of the raw wastewater ranged from 0.106-0.279 mg/L. The overall conditions were very much favorable even at high organic loading and minimum retention time. It is therefore concluded that the system is practically feasible for the treatmentof wastewater containing high content of organic matter

Impacts of Competitive Inhibition, Parent Compound Formation and Partitioning Behavior on the Removal of Antibiotics in Municipal Wastewater Treatment

We present a process model that predicts the removal of the antibiotic micropollutants, sulfamethoxazole (SMX), tetracycline (TCY), and ciprofloxacin (CIP), in an activated sludge treatment system. A novel method was developed to solve the inverse problem of inferring process rate, sorption, and correction factor parameter values from batch experimental results obtained under aerobic and anoxic conditions. Instead of spiking the batch reactors with reference substances, measurements were made using the xenobiotic organic micropollutant content of preclarified municipal sewage. Parent compound formation and removal were observed, and the model developed using the simulation software West showed limited efficiency to describe the selected micropollutants profiles, when growth substrate removal occurs. The model structure was optimized by accounting for competitive inhibition by readily biodegradable substrates on the cometabolic micropollutant biotransformation processes. Our results suggest that, under anoxic conditions, hydrophobicity-independent mechanisms can significantly impact solid-liquid partitioning that our model takes into account by using the sorption coefficient as a lumped parameter. Forward dynamic simulations were carried out to evaluate the developed model and to confirm it for SMX using data obtained in a full-scale treatment plant. Evaluation of measured and simulation results suggest that, robust model prediction can be achieved by approximating the influent load of chemicals biodegrading via a given parent compound, e.g., human conjugates, as an antibiotic mass that is proportional to the parent compound load.

Operating costs related to instability in a pulp and paper activated sludge treatment system

Wastewater treatment by the activated sludge treatment process has been widely implemented in the pulp and paper industry; however, this process can be difficult to operate, particularly during sludge bulking events. Preventing noncompliance events can normally be achieved effectively in wastewater treatment plants (WWTP) by manual control, but this can be costly. Indeed, the use of various relief chemical products constitutes a significant part of a WWTP’s operating costs. Moreover, the use of these reactive rather than proactive methods does not target the specific causes of problems and only temporarily removes their effects. This paper analyzes the operating costs of an activated sludge process treating the effluent from a thermomechanical pulp mill in eastern Canada, in particular the costs associated with abnormal or transient system behavior. A specific treatment cost of $725/t BOD was calculated, highlighting the importance of chemical products, particularly for sludge thickening and settling, and of energy. Costs associated with instability were also reported, and it was found that 11.0% of the total operating costs were directed at relieving the treatment system from an unstable state.