Effluent Soluble Chemical Oxygen Demand Research Articles

Modeling of two-stage anaerobic onsite wastewater sanitation system to predict effluent soluble chemical oxygen demand through machine learning

The present research aims to predict effluent soluble chemical oxygen demand (SCOD) in anaerobic digestion (AD) process using machine-learning based approach. Anaerobic digestion is a highly sensitive process and depends upon several environmental and operational factors, such as temperature, flow, and load. Therefore, predicting output characteristics using modeling is important not only for process monitoring and control, but also to reduce the operating cost of the treatment plant. It is difficult to predict COD in a real time mode, so it is better to use Complex Mathematical Modeling (CMM) for simulating AD process and forecasting output parameters. Therefore, different Machine Learning algorithms, such as Linear Regression, Decision Tree, Random Forest and Artificial Neural Networks, have been used for predicting effluent SCOD using data acquired from in situ anaerobic wastewater treatment system. The result of the predicted data using different algorithms were compared with experimental data of anaerobic system. It was observed that the Artificial Neural Networks is the most effective simulation technique that correlated with the experimental data with the mean absolute percentage error of 10.63 and R2 score of 0.96. This research proposes an efficient and reliable integrated modeling method for early prediction of the water quality in wastewater treatment.

Molecular insights into the dissolved organic matter of leather wastewater in leather industrial park wastewater treatment plant

Leather wastewater (LW) effluent is characterized by complex organic matter, high salinity, and poor biodegradability. To meet the discharge standards, LW effluent is often mixed with municipal wastewater (MW) before being treated at a leather industrial park wastewater treatment plant (LIPWWTP). However, whether this method efficiently removes the dissolved organic matter (DOM) from LW effluent (LWDOM) remains debatable. In this study, the transformation of DOM during full-scale treatment was revealed using spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. LWDOM exhibited higher aromaticity and lower molecular weight than DOM in MW (MWDOM). The DOM properties in mixed wastewater (MixW) were similar to those in LWDOM and MWDOM. The MixW was treated using a flocculation/primary sedimentation tank (FL1/PST), anoxic/oxic (A/O) process, secondary sedimentation tank (SST), flocculation/sedimentation tank, denitrification filter (FL2/ST-DNF), and an ozonation contact reactor (O3). The FL1/PST unit preferentially removed the peptide-like compounds. The A/O-SST units had the highest removal efficiencies for dissolved organic carbon (DOC) (61.34 %) and soluble chemical oxygen demand (SCOD) (52.2 %). The FL2/ST-DNF treatment removed the lignin-like compounds. The final treatment showed poor DOM mineralization efficiency. The correlation between water quality indices, spectral indices, and molecular-level parameters indicated that lignin-like compounds were strongly correlated with spectral indices and CHOS compounds considerably contributed to the SCOD and DOC. Although the effluent SCOD met the discharge standard, some refractory DOM from LW remained in the effluent. This study illustrates the composition and transformation of DOM and provides theoretical guidance for improving the current treatment processes.

The Pilot Study of the Influence of Free Ammonia on Membrane Fouling during the Partial Nitrosation of Pig Farm Anaerobic Digestion Liquid.

The problem of membrane fouling is a key factor restricting the application of the membrane bioreactor (MBR) in the partial nitrosation (PN) and anaerobic ammonia oxidation (anammox) processes. In this study, the pilot-scale continuous flow MBR was used to start up the partial nitrosation process in order to investigate the change trend of mid-transmembrane pressure (TMP) in the process of start-up, which was further explored to clarify the membrane fouling mechanism in the pilot-scale reactor. The results showed that the MBR system was in a stable operating condition during the partial nitrosation operation and that the online automatic backwash operation mode is beneficial in alleviating membrane fouling and reducing the cost of membrane washing. Particular attention was paid to the influence trend of free ammonia (FA)on membrane fouling, and it was found that the increase in FA concentration plays the most critical role in membrane fouling. The increase in FA concentration led to an increase in the extracellular polymer (EPS), dissolved microorganism product (SMP) and soluble chemical oxygen demand (SCOD) concentration. FA was extremely significantly correlated with EPS and SCOD, and the FA concentration was approximately 20.7 mg/L. The SCODeff (effluent SCOD concentration) concentration was approximately 147 mg/L higher than the SCODinf (influent SCOD concentration) concentration. FA mainly affects membrane fouling by affecting the concentration of EPS and SCOD.

Kinetic assessment of the anaerobic treatment of piggery wastewaters using an EGSB reactor with Cuban natural zeolite

Large pig farms generate enormous volumes of wastewater without proper treatment before discharge. High-rate anaerobic reactors as the expanded granular sludge bed (EGSB) are rarely reported for that purpose. In this study, an EGSB reactor with Cuban natural zeolite addition was evaluated for treating piggery wastewaters at lab scale. This study was conducted at different organic loading rate (OLR) ranging from 0.32 to 6.13 gCOD/Ld with a constant hydraulic retention time (HRT) of 12 h. The evolution of several control and operational parameters as the soluble chemical oxygen demand (COD) demonstrated a proper bioreactor performance to treat piggery wastewater. The results showed that the addition of natural zeolite at 40 gzeo/Lreactor in EGSB reactor results in COD efficiencies over 70%, despite of the fluctuations of fed wastewater characteristics. The kinetic study demonstrates that, the modified Stover-Kincannon model was found to be appropriate for EGSB reactor. The effluent soluble COD was predicted with high determination coefficient. The maximum removal rate constant (Umax) and saturation value constant (KB) were reported for a first time for the EGSB reactor with values of 10.2 and 11.8 gCOD/Ld, respectively. Methane yield for both, batch and continues experiments, were in the range from 214.5 to 299.8 mLCH4/gCOD.

Effect of ozonation as pre-treatment and polishing step on removal of ecotoxicity and alkylphenol ethoxylates from tank truck cleaning wastewater

Wastewater originating from tank truck cleaning (TTC) industry is reputed for its large variability and may lead to emission of recalcitrant and ecotoxic substances in discharge waters. In this study, TTC wastewater was biologically treated in two lab-scale activated sludge sequencing batch reactors. Two strategies were used, (1) influent pre-treatment with ozone followed by activated sludge treatment and (2) activated sludge treatment followed by polishing with ozone. Effluent soluble chemical oxygen demand (sCOD), ecotoxicity and the 4-nonylphenol (NP) concentration were used to evaluate and compare both strategies. Experiments were conducted for two different TTC companies using the same set-up. For Company 1, a decrease in ecotoxicity of 80 % was observed for algal growth inhibition and 10 % for Daphnia immobilization when using effluent polishing compared to pre-treatment. Hereby the NP concentration decreased below discharge limits (0.3 ng.mL−1). For Company 2 the ecotoxic effect in the algal growth inhibition test increased to 100 % when conducting effluent polishing, while ecotoxicity for the original effluent and the effluent from the pre-treated system were similar. sCOD did not decrease significantly and the discharge limit of NP was only met for one sample. Extended (7 h) effluent ozone polishing tests were conducted at two pH setpoints to assess the impact of radical formation during ozone treatment. In general, it was observed that ozone as a pre-treatment step had no significant influence on ecotoxicity and COD removal. Effluent polishing can improve ecotoxicity and effluent characteristics, despite the dependence on wastewater composition, as toxic side products may be produced.

Two- vs. single-stage anaerobic reactors: evaluation of effluent quality and energy production potential using sucrose-based wastewater

Two- and single-stage anaerobic treatment systems were assessed for treatment performance and for bioenergy production from sucrose-based wastewater. In the two-stage system, a hydrogen-producing upflow anaerobic sludge blanket reactor (HU reactor) was used in the acidogenic phase. The methanogenic reactor of the two-stage system (MF reactor) and the single-stage reactor (SSF reactor) were structured fixed-bed reactors. The two-stage system showed superior performance, evidenced by lower organic acids, chemical oxygen demand (COD) and suspended solids concentrations in the effluent, and higher biogas methane content and yield. Continuous and stable H2 production was obtained in the acidogenic reactor. At the end of operation, the organic loading rates applied to the two- and single-stage systems were 6.4 and 5.2 gCOD L-1 d-1, respectively. Under these conditions, the effluent soluble COD and volatile suspended solids (VSS) concentrations were 165 and 92 mg L-1 in the two-stage system, and 256 and 244 mg L-1 in the single-stage system, respectively. The energy yield of the two-stage system was 20.69 kJ g-1CODadded, which was 34% higher than the yield of the single-stage system. The sequencing analyses showed that the archaeal distribution changed little between the inoculum and sludge from the MF reactor, in which acetoclastic Methanosaeta was predominant. However, hydrogenotrophic Methanospirillum was found most, followed by Methanosaeta, in the sludge from the SSF reactor.

Which activated sludge configurations qualify for maximizing energy conservation – Why?

AbstractBACKGROUNDThis paper aimed to provide a critical appraisal on maximizing sludge generation and energy conservation in high‐rate activated sludge (AS) configurations. The role of gravity settling and the positive attributes of high rate membrane bioreactors were emphasized. The appraisal covered data reported in the literature on 40 different experiments testing high‐rate AS configurations for sludge generation and energy conservation.RESULTSIn systems with gravity settling, effluent chemical oxygen demand (COD) was higher than 125 mg L−1 in 60% of the experiments, with similarly high effluent soluble COD values. In high‐rate MBR systems, permeate COD fluctuated around 12–18 mgCOD L−1; in gravity systems, COD loss in the effluent was higher than 200 mg L−1 in 17 runs (65%) and 300 mg L−1 in 12 runs (46%). Corresponding observed yields were only 9–43%. Membrane systems consistently yielded much higher observed yields of 50–60%.CONCLUSIONFor energy recovery, AS systems require a major transition, reducing the sludge age to 1.0–2.0 d; only high‐rate systems are capable of maximizing energy conservation. This argument does not apply to the contact stabilization process, which is inherently unsuitable for energy recovery. A transition is also needed to replace gravity settling by membrane systems for effective control of particulate and soluble COD components. © 2018 Society of Chemical Industry

Membrane Fouling Characteristics of a Side-Stream Tubular Anaerobic Membrane Bioreactor (AnMBR) Treating Domestic Wastewater

A lab-scale of a side stream anaerobic membrane bioreactor (AnMBR) equipped with a tubular membrane operated at the mesophilic temperature of 37.0 ± 1.2 °C for treating domestic wastewater was tested to investigate its performance and fouling characteristics at two organic loading rates (OLR) of 0.25 kg COD m−3d−1, and 0.70 kg COD m−3d−1, respectively. The AnMBR was operated for 600 days at sludge retention time (SRT) of 100 days. This AnMBR exhibits excellent chemical oxygen demand (COD) removal of 91% at 0.25 kg COD m−3d−1, and 94% at 0.7 kg COD m−3d−1 respectively, with effluent-soluble COD below 50 mg/L. Chemically-enhanced cleaning method using NaOH, NaOCl, and citric acid solution were introduced for fouling investigation at these two stages. The results showed that sequential chemical cleaning of alkaline and acid were most effective to recover the membrane flux. The alkaline cleaning was effective at removing organic foulants, while citric acid cleaning was effective at removing the scalants. The analyses of the excitation emission matrix, gel permeation chromatography, and extracellular polymeric substances indicated that major components of membrane foulants were proteins, carbohydrates, humic, and fulvic acids. At 0.25 kg COD m−3d−1, organic fouling was more prone to be trapped in the cake layers and responsible for membrane pore blockage, inorganic fouling exhibited marginal contribution to the membrane fouling behavior. However, at 0.70 kg COD m−3d−1, high concentrations of organic and inorganic foulants supported an essential role of organic and inorganic fouling on membrane fouling behavior.

Transesterification of Waste Activated Sludge for Biosolids Reduction and Biodiesel Production

Transesterification of waste activated sludge (WAS) was evaluated as a cost-effective technique to reduce excess biosolids and recover biodiesel feedstock from activated sludge treatment processes. A laboratory-scale sequencing batch reactor (SBR) was operated with recycling transesterification-treated WAS back to the aeration basin. Seventy percent recycling of WAS resulted in a 48% reduction of excess biosolids in comparison with a conventional SBR, which was operated in parallel as the control SBR. Biodiesel recovery of 8.0% (dried weight basis) was achieved at an optimum transesterification condition using acidic methanol and xylene as cosolvent. Average effluent soluble chemical oxygen demand (COD) and total suspended solids (TSS) concentrations from the test SBR and control SBR were comparable, indicating that the recycling of transesterification-treated WAS did not have detrimental effect on the effluent quality. This study demonstrated that transesterification and recycling of WAS may be a feasible technique for reducing excess biosolids, while producing valuable biodiesel feedstock from the activated sludge process.

Biohydrogen Production as Clean Fuel from physically Pretreated Mixed Culture.

Background:Due to depletion of fossil fuel reserves, global warming, and the need for energy efficiency, the new energy resource is required. For this purpose, hydrogen can be considered as clean and efficient energy carrier. In this study, biohydrogen production from physical pretreated mixed culture was investigated.Materials and Methods:In this study, the optimal conditions for physical pretreatment of mixed culture were investigated for the enrichment of hydrogen-producing bacteria (HPB). Three individual pretreatment processes, including thermal, ultraviolet (UV) radiation, and ultrasonication (US) were conducted in batch tests. The batch tests were carried out via 500 mL glass flasks with working volume 400 mL. Glucose was used as sole substrate, and other essential nutrient and trace elements were added. To agitation of substrate with HPB inoculum, the magnet stirrer was used at 60 rpm.Results:The results showed the production of H2 gas could be increased by appropriate pretreatment methods including thermal pretreatment at 100°C. At 100°C as a pretreatment, the volume of H2 gas was 112.25 mL and followed by US (97.46 mL), UV (89.11 mL), 80°C (72.72 mL), 90°C (53.95 mL), and 70°C (26.01 mL). In the pretreatment methods, the solution pH and effluent soluble chemical oxygen demand was 6.3–6.7 and 5100–8300 mg/L, respectively.Conclusions:The Gompertz model depicts that all R2 values were more than 0.93, indicating that the fitted curves were best fitted with the experimental points.

Alkaline and acid thermal hydrolysis of biological excess sludge in sequencing batch reactor

The efficiency of biological wastewater treatment processes is based on pH sensitivity which leads to the reduction in the amount of sludge production. In order to achieve the best result, thermal hydrolysis is recognized and used, although acid thermal hydrolysis has serious drawbacks (corrosion, required post-neutralization, etc.). Alkaline thermal hydrolysis has been less remarkable, as the subject of the detailed pilot-scale research of two sequencing batch reactors (SBR) reported in this study. Long-term (about 8 months) continuous experiments were conducted to identify the effect of pH increasing from 4 to 11 in controlled temperature of 60°C to achieve the optimum pH for the reduction of excess biological sludge. After providing a steady state in the reactors, sampling and testing parameters including chemical oxygen demand (COD), mixed liquor suspended solids (MLSS), dissolved oxygen (DO), specific oxygen uptake rate (SOUR), sludge volume index (SVI), and yield (Y) coefficient were evaluated. Results showed that in pH of 9, the kinetic yield coefficient decreased from 0.63 to 0.33. Therefore, excess sludge declined to 44%. Moreover, the soluble COD increased slightly in the effluent, whereas the removal percentage decreased to 79 in the reactor while the amount of SVI and SOUR in this pH dropped to 65 mg/l and 12 mgO2/l.g VSS, respectively. However, no sludge was seen in the higher pH or lower pH, whereas effluent soluble chemical oxygen demand (SCOD) and turbidity was increased. Additionally, the wastewater disposal standards were not achieved and had a bad odor.

Tolerance response to in situ ammonia stress in a pilot-scale anaerobic digestion reactor for alleviating ammonia inhibition

The anaerobic digestion (AD) of protein-rich substrates is generally inhibited by ammonia. In this study, ammonia-tolerant acclimation was exposed to a stepwise in situ ammonia stress during the continuous AD of solid residual kitchen waste by using a continuous stirred tank reactor with a 50L active volume. The reactor worked well during the acclimation process, with an average daily biogas production of 58L/d, an effluent soluble chemical oxygen demand of 7238mg/L, a volatile fatty acid (VFA) content of 578mg/L, and a VFA/alkalinity ratio of less than 0.4. Moreover, ammonia stress enhanced the activity of Coenzyme F420. The results of high-throughput 16S rDNA sequencing showed that ammonia stress increased the relative abundance of Firmicutes bacteria and hydrogenotrophic methanogens but decreased the abundance of acetotrophic methanogens. This microbial community shift was proposed to be an in situ response strategy for ammonia stress adaptation.

Modeling of organic substrate transformation in the high-rate activated sludge process.

This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to particulate COD. The adsorbed organics are then converted through hydrolysis to the slowly biodegradable soluble fraction. Two soluble substrate models were evaluated during this study, i.e., the dual substrate and the diauxic models. Both models used two state variables for biodegradable soluble substrate (SBf and SBs) and a single biomass population. The A-stage pilot typically removed 63% of the soluble substrate (SB) at an SRT <0.13 d and 79% at SRT of 0.23 d. In comparison, the dual substrate model predicted 58% removal at the lower SRT and 78% at the higher SRT, with the diauxic model predicting 32% and 70% removals, respectively. Overall, the dual substrate model provided better results than the diauxic model and therefore it was adopted during this study. The dual substrate model successfully described the higher effluent soluble COD observed in the HRAS systems due to the partial removal of SBs, which is almost completely removed in higher SRT systems.

The effect of continuous Zn (II) exposure on the organic degradation capability and soluble microbial products (SMP) of activated sludge

This study describes the change of organic degradation capability and soluble microbial products (SMP) generated in activated sludge under continuous exposure to Zn (II) in a sequencing batch reactor (SBR). In 338 days of operation, the added Zn (II) concentrations were gradually increased from 50 to 100, 200, 400 to 600 and 800mg/L. Results showed that after adaptation, the activated sludge could endure 400mg/L Zn (II) without showing evident reduction in organic degradation ability (92±1% of chemical oxygen demand (COD) removal in stable state). However, when 600 and 800mg/L Zn (II) were applied, the effluent water quality significantly deteriorated. Meanwhile, under increasing Zn (II) concentrations, the SMP content in the activated sludge, together with its main biochemical constituents, first increased slightly below 400mg/L of Zn (II), then rose sharply under 600 and 800mg/L Zn (II). Furthermore, a close correlation was found between SMP content and effluent soluble COD in both the Experimental Reactor and Control Reactor. In addition, the Zn (II) concentrations in the effluent and SMP extraction liquid were further analyzed and discussed to reveal the role that SMP constituents played in defense and resistance to the toxicity of Zn (II).

Development of mechanistically based model for simulating soluble microbial products generation in an aerated/non-aerated SBR

Soluble microbial products (SMPs) are considered as the main organic components in wastewater treatment plant effluent from biological wastewater treatment systems. To investigate and explore SMP metabolism pathway for further treatment and control, two innovative mechanistically based activated sludge models were developed by extension of activated sludge model no.3 (ASM3). One was the model by combining SMP formation and degradation (ASM3-SMP model) processes with ASM3, and the other by combining both SMP and simultaneous substrate storage and growth (SSSG) mechanisms with ASM3 (SSSG-ASM3-SMP model). The detailed schematic modification and process supplements were introduced for comprehensively understanding all the mechanisms involved in the activated sludge process. The evaluations of these two models were demonstrated by a laboratory-scale sequencing batch reactor (SBR) operated under aerated/non-aerated conditions. The simulated and measured results indicated that SMP comprised about 83% of total soluble chemical oxygen demand (SCOD) in which biomass-associated products (BAPs) were predominant compared with utilization-associated products (UAPs). It also elucidated that there should be a minimum SMP value as the reactive time increases continuously and this conclusion could be used to optimize effluent SCOD in activated sludge processes. The comparative results among ASM3, ASM3-SMP and SSSG-ASM3-SMP models and the experimental measurements (SCOD, ammonia and nitrate nitrogen) showed clearly the best agreement with SSSG-ASM3-SMP simulation values (R=0.993), strongly suggesting that both SMP formation and degradation and SSSG mechanisms are necessary in biologically activated sludge modeling for municipal wastewater treatment.

Minimum Requirements for Trace Metals (Iron, Nickel, Cobalt, and Zinc) in Thermophilic and Mesophilic Methane Fermentation from Glucose

The minimum requirements for four essential trace metals were examined in both thermophilic and mesophilic methane fermentation of glucose. The minimum requirement here was defined as the amount that supports the effluent soluble chemical oxygen demand (COD) of 1000 mg/ L or less for the duration of several times the hydraulic retention time (HRT). For this purpose, completely mixed reactors were run semi-continuously at 5 days HRT, with 10 g/L substrate COD. The minimum requirements determined as milligrams per gram COD removed were 0.45, 0.049, 0.054, and 0.24 in the thermophilic system and 0.20, 0.0063, 0.017, and 0.049 in the mesophilic system for iron, nickel, cobalt, and zinc, respectively. The thermophilic system required larger amounts (2.2 to 7.8 times) of the trace metals than the mesophilic system, indicating greater assimilation by biomass and/or less bioavailability under thermophilic conditions. The results can give quantitative information on trace metal nutrition for successful methane fermentation.

Comparative Performance of A2 /O and a Novel Membrane-Bioreactor-Based Process for Biological Nitrogen and Phosphorus Removal

The comparison between a novel membrane bioreactor (MBR) system and a conventional anaerobic-anoxic-aerobic (A2/O) system was conducted using synthetic wastewater (SWW) and municipal wastewater (MWW). Each system was operated at an overall hydraulic retention time of 8 hours and solids retention time of 10 days. The MBR exhibited better overall system performance than the A2/O system, in terms of phosphorus removal. Nitrogen removal efficiencies were close in the two systems at 73 to 74% in both runs, while phosphorus removal efficiencies were 96 and 74% (SWW run) and 80 and 75% (MWW run), for the MBR and A2/O, respectively. Effluent soluble chemical oxygen demand (COD) was less than 15 mg/L in the two systems during both runs. Phosphorus uptake by denitrifying phosphate-accumulating organisms accounted for 49% of the total uptake in the MBR compared with 33% in the A2/O during the SWW run. The dynamic test clearly showed that the MBR had better denitrification capacity than the A2/O system. The MWW run indicated that MBR ferments particulate COD better than A2/ O. The effect of the intermediate clarifier on MBR phosphorus removal was significant, with phosphorus uptake of 0.16 g/d in the SWW run and phosphorus release of 0.08 g/d in the MWW run, thus enhancing thetotal phosphorus removal in both cases.

Respirometric evaluation of biodegradation characteristics of dairy wastewater for organic carbon removal

This study evaluates the biodegradation kinetics of an integrated dairy wastewater, with the main purpose of defining the experimental basis for modelling of the activated sludge process. Besides conventional characterization, the experiments involved detailed chemical oxygen demand (COD) fractionation and assessment of major kinetic and stoichiometric coefficients, by using respirometric methods. A multi‐component model based on the endogenous decay concept was used for the kinetic interpretation. The results of conventional analyses and respirometric evaluations together with the assessment of residual components showed that the organic carbon content of the dairy wastewater was mostly soluble and biodegradable. The soluble, slowly biodegradable COD was the major COD fraction, representing around 50% of the total COD. Model calibration of the oxygen uptake rate profiles were consistent and revealed the existence of dual hydrolysis kinetics for soluble and particulate COD components. The hydrolysis rate associated with the main COD component – the soluble, slowly biodegradable COD fraction – was found to be 1.2 d−1, which is quite low and underlines the role of this COD fraction as the rate‐limiting factor for effluent quality. Simulation of process efficiency by the adopted model, calibrated with the experimentally determined parameters, indicated that effective control of the biodegradation of the soluble biodegradable COD components could be done by selection of appropriate values for the sludge age and hydraulic retention time. In this way, the total effluent soluble COD level could be lowered to 30–40 mg L−1 range, in conformity with effluent limitations.

Fate of LCFA in the co-digestion of cow manure, food waste and discontinuous addition of oil

Different concentrations of oily waste were added in a discontinuous mode and recurrently to anaerobic continuous stirred tank reactors fed with cow manure and food waste. Four continuous stirred tank reactors were run in parallel. A control reactor (R1) received no additional oil and R2, R3 and R4 received increasing concentrations of oil in two different experimental approaches. First, the lipids composition was forced to change suddenly, in three moments, without changing the total chemical oxygen demand (COD) fed to the reactors. The only long chain fatty acid (LCFA) detected onto the R1 solid matrix was palmitic acid (C16:0). Nevertheless in the solid matrix of R2, R3 and R4 C16:0 and stearic acid were detected. For occasional increase in the oil concentration up to 7.7 gCOD oil/L reactor (55% Oil COD/Total COD) no statistical differences were detected between the reactors, in terms of methane production, effluent soluble COD, effluent volatile fatty acids and total and volatile solids removal. Therefore this experiment allowed to conclude that cow manure–food waste co-digestion presents sufficient buffer capacity to endure solid-associated LCFA concentration up to 20–25 gCOD-LCFA/kgTS. In a second experiment higher concentrations of oil were added, raising occasionally the concentration in the reactors to 9, 12, 15 and 18 gCOD oil/L reactor. All pulses had a positive effect in methane production, with the exception of the highest oil pulse concentration, that persistently impaired the reactor performance. This experiment demonstrates that threshold values for LCFA and C16:0 accumulation onto the solid matrix, of about 180–220 gCOD-LCFA/kgTS and 120–150 gCOD-C16:0/kgTS, should not be surpassed in order to prevent persistent reactor failure, as occurs in some full scale co-digestion plants.

An activated sludge model based on activated sludge model number 3 for full‐scale wastewater treatment plant simulation

A modified model based on the activated sludge model no. 3 was established to simulate a full‐scale municipal wastewater treatment plant in Shanghai, China. The activated sludge model no. 3 was modified to describe the simultaneous storage and growth processes occurring in activated sludge systems under aerobic and anoxic conditions. The mechanism of soluble microbial product formation and degradation by microorganisms was considered in this proposed model. Three months simulation was conducted including soluble chemical oxygen demand, NH4 +‐N, NOX −‐N and T–N parameters, and compared with measured data from the Quyang wastewater treatment plant. Results indicated that the calculated effluent chemical oxygen demand and NH4 +‐N using this proposed model were in good agreement with the measured data. Results also showed that besides inert soluble organic matter contributing to the effluent chemical oxygen demand, soluble microbial products played an important part in the effluent chemical oxygen demand and, therefore, demonstrated that these products composed an important portion of effluent soluble chemical oxygen demand in wastewater treatment plants and should not be neglected.