COD Loading Research Articles

Contribution of siloxanes to COD loading at wastewater treatment plants: Phase transfer, removal, and fate at different treatment units

Cyclic volatile methylsiloxanes (cVMSs) are entering to waste stream in increasing quantities due to their increasing use in personal care products (i.e., shampoos, creams). The cVMSs have high vapor pressures and low solubilities and are mostly transferred into the gaseous phase via volatilization; however, some are sorbed onto biosolids. The purpose of this study was to track and estimate the phase transfer (water, solids, gas), fate, and contribution to COD loading of selected siloxanes (D4, D5 and D6) which are the most commonly found cVMSs in the wastewater systems. Removal efficiencies of the wastewater treatment units were evaluated based on the partitioning characteristics of the cVMSs in gas, liquid, and biosolids phases. The contributions of the siloxanes present in the influent and effluent were estimated in terms of COD levels based on the theoretical oxygen demand (ThOD) of the siloxanes. Siloxanes constitute approximately 39 and 0.001mgL−1 of the COD in the influents and effluent. Oxidation systems showed higher removal efficiencies based COD loading in comparison to the removal efficiencies achieved aeration tanks and filtration systems. Treatment systems effectively remove the siloxanes from the aqueous phase with over 94% efficiency. About 50% of the siloxanes entering to the wastewater treatment plant accumulate in biosolids.

The biomass fraction of phosphate-accumulating organisms grown in anoxic environment in an enhanced biological phosphorus removal (EBPR) system

To improve the design and performance of anoxic phosphorus uptake process, the biomass fractions of PAOs grown in anoxic environment and denitrification rate, with PHAs as carbon source, was investigated in a pilot scale study of EBPR system which was based on stoichiometry and mass balance. The system, containing Modified University of Cape Town (MUCT) reactor, was maintained at steady state with COD loading of 0.25 kg COD/(kg MLVSS d), and solid retention time (SRT) of 12 d. Based on mass balance calculation, 46.74% of organic matter, 50.95% of nitrogen, and 42.03% of phosphorus in the influent were converted to carbon dioxide, nitrogen gas, and poly-phosphate, respectively. In the second anoxic stage, the biomass yield of PAOs with nitrate as electron acceptor was 4.90 gC5H7O2N/d, and its yield fraction was 20.63%. For the reaction to proceed properly, 10.48 g PHA/d of PHAs was oxidized, and 3.68 g NO3--N/d of nitrate was reduced. The denitrification rate with PHAs as carbon source was 0.058 kg NO3--N/(kg MLVSS·d). These results showed that a higher amount of PAO growth under anoxic condition was observed in the MUCT system, and 0.058 kg NO3--N/(kg MLVSS·d) of the denitrification rate with PHAs could be used as the reference values for calculation of anoxic stage volume.

Optimization of separate hydrogen and methane production from cassava wastewater using two-stage upflow anaerobic sludge blanket reactor (UASB) system under thermophilic operation

The objective of this study was to investigate the separate hydrogen and methane productions from cassava wastewater by using a two-stage upflow anaerobic sludge blanket (UASB) system under thermophilic operation. Recycle ratio of the effluent from methane bioreactor-to-feed flow rate was fixed at 1:1 and pH of hydrogen UASB unit was maintained at 5.5. At optimum COD loading rate of 90kg/m3d based on the feed COD load and hydrogen UASB volume, the produced gas from the hydrogen UASB unit mainly contained H2 and CO2 which provided the maximum hydrogen yield (54.22mlH2/g COD applied) and specific hydrogen production rate (197.17ml/gMLVSSd). At the same optimum COD loading rate, the produced gas from the methane UASB unit mainly contained CH4 and CO2 without H2 which were also consistent with the maximum methane yield (164.87mlCH4/g COD applied) and specific methane production rate (356.31mlCH4/gMLVSSd). The recycling operation minimized the use of NaOH for pH control in hydrogen UASB unit.

The effect of COD loading on the granule-based enhanced biological phosphorus removal system and the recoverability

In this study, the effect of varied COD loading (200, 400, 500, 600 and 800mgL−1) on stability and recoverability of granule-based enhanced biological phosphorus removal (EBPR) system was investigated during continuously 53-d operation. Results showed that COD loading higher than 500mgL−1 could obviously deteriorate the granular EBPR system and result in sludge bulking with filamentous bacteria. High COD loading also changed the transformation patterns of poly-β-hydroxyalkanoates (PHAs) and glycogen in metabolism process of polyphosphate-accumulating organisms (PAOs) and inhibited the EPS secretion, which completely destroyed the stability and integrality of granules. Results of FISH indicated that glycogen-accumulating organisms (GAOs) and other microorganisms had a competitive advantage over PAOs with higher COD loading. The community composition and EBPR performance were recovered irreversibly in long time operation when COD loading was higher than 500mgL−1.

Simultaneous Production of Hydrogen and Methane from Cassava Wastewater Using a Two Stage Upflow Anaerobic Sludge Blanket System Under Thermophilic Operation

The objective of this study was to investigate the hydrogen and methane production from cassava wastewater by using a two stage upflow anaerobic sludge blanket (UASB) system under thermophillic operation (55 °C). The recycle ratio of the effluent from the methane bioreactor-to-the feed flow rate was fixed at 1:1 and the solution pH in the hydrogen bioreactor was maintained at 5.5 by a pH controller while the solution pH of the methane bioreactor was not controlled. The liquid working volumes of the hydrogen and methane bioreactors were 4 and 24 L, respectively. The two stage UASB system was operated at different COD loading rates (30, 60, 90, 120, and 150 kg/m 3 d based on the hydrogen bioreactor volume). Under the optimum COD loading rate of 90 kg/m 3 d based on the hydrogen bioreactor volume corresponding to 15 kg/m 3 d based on the methane bioreactor volume for the hydrogen bioreactor, the produced gas contained 40 % H2, 52 % CO2 and 8 % CH4 and the system provided a maximum hydrogen yield and specific hydrogen production rate of 18 mL/g COD removed and 520 mL/L d, respectively. Under this optimum COD loading rate, the produced gas of the methane bioreactor contained 65 % CH4 and 35 % CO2 without hydrogen and the system provided a maximum methane yield and specific methane production rate of 115 mL/g COD removed and 650 mL/L d, respectively. The operation of recycling from methane bioreactor to hydrogen bioreactor optimized the use of NaOH for pH control in the hydrogen production step.

The Research of Wastewater Treatment by Membrane Bioreactor (MBR)

Membrane bioreactor is a combination of membrane and sewage biological treatment technology, which is the new wastewater treatment technology .In this paper, the effect of pH and NH3-N load on membrane bioreactor for wastewater treatment is studied. Through the use of artificial mixed wastewater experiments,the results are as follows:The effect of pH on the effluent COD is not obvious, on the removal of NH3-N is very large. Taking into account of removal of organics and NH3-N, the pH should be controlled at 8.0.The removal rate of NH3-N decreased significantly with the increase of the NH3-N load. When the NH3-N load is 0.023 Kg/m3· d, the removal rate reach the maximum value. In this case,the load of COD is 1.1 Kg/ m3.d.

Combined hydrolysis acidification and bio-contact oxidation system with air-lift tubes and activated carbon bioreactor for oilfield wastewater treatment

This paper investigated the enhancement of the COD reduction of an oilfield wastewater treatment process by installing air-lift tubes and adding an activated carbon bioreactor (ACB) to form a combined hydrolysis acidification and bio-contact oxidation system with air-lift tubes (HA/air-lift BCO) and an ACB. Three heat-resistant bacterial strains were cultivated and subsequently applied in above pilot plant test. Installing air-lift tubes in aerobic tanks reduced the necessary air to water ratio from 20 to 5. Continuous operation of the HA/air-lift BCO system for 2months with a hydraulic retention time of 36h, a volumetric load of 0.14kgCOD/(m3d) (hydrolysis-acidification or anaerobic tank), and 0.06kgCOD/(m3d) (aerobic tanks) achieved an average reduction of COD by 60%, oil and grease by 62%, total suspended solids by 75%, and sulfides by 77%. With a COD load of 0.56kg/(m3d), the average COD in the ACB effluent was 58mg/L.

Changes in the microbial community during the acclimation stages of the methane fermentation for the treatment of glycerol

Granular sludge from a full-scale methane reactor treating brewery wastewater was used as a seed for the treatment of glycerol in a laboratory-scale repeated-batch methane reactor, and the change in the microbial community during the acclimation stages was examined. Two types of substrate solutions, a glucose, sodium acetate, and lactic acid mixture, as well as glycerol, were prepared and fed by mixing the two solutions to increase the ratio, in a stepwise manner, of glycerol from 0% to 100%, while keeping a loading of COD at 2.5 kg m−3 d−1 throughout the fermentation process. Vigorous methane gas production, approximately 580 dm3 m−3 d−1, was observed during the acclimation stages. Microbial analysis revealed that both bacterial and archaeal communities changed significantly; bacteria (genus Trichococcus and family Syntrophomonadaceae) became dominant rapidly after the start of acclimation, and archaea belonging to the hydrogenotrophic methanogens (genera Methanobacterium and Methanospirillum), increased gradually with the progress of acclimation.

Continuous electricity generation with piggery wastewater treatment using an anaerobic baffled stacking microbial fuel cell

Anaerobic baffled stacking microbial fuel cells (ABSMFCs) consisting of four individual MFCs with total volume of 6.4 L was constructed to generate electricity from piggery wastewater in present study. Anode materials (carbon paper, carbon fiber felt, and graphite granule) and anode connecting modes of the four MFCs (in series or parallel) could affect the bioelectricity generation and wastewater treatment effects. When they were connected in series, voltage loss occurred and voltage reversed with increase in current between some MFCs. The influent COD loadings showed significant relationship to the performance of ABSMFC, as it increased from 0.2 to 4.0 g/L d, voltage output across an external resistance of 1,000 Ω decreased by 71.7% (in series) and 30.7% (in parallel), respectively; coulombic efficiency decreased rapidly by 96.7% (in series) and 94.3% (in parallel), while COD removal efficiency initially increased and then decreased. This study demonstrated that the large volume ABSMFC can realize stable power output associated with piggery wastewater treatment and is suitable to scale-up for actual application.

Enhanced reductive transformation of p-chloronitrobenzene in a novel bioelectrode–UASB coupled system

The laboratory-scale upflow anaerobic sludge blanket (UASB) reactor equipped with a pair of bioelectrodes was established for the enhancement of p-chloronitrobenzene (p-ClNB) reductive transformation via the electrolysis. Results showed that a stable COD removal efficiency over 99% and high p-ClNB transformation rate of 0.328h−1 were achieved in the bioelectrode–UASB coupled system with influent COD and p-ClNB loading rates of 2.1–4.2kgCODm−3d−1 and 60gm−3d−1, respectively. The bioelectrodes were supplied with a voltage of 2.5–5.0V and the effective current was above 2mA, which resulted in a continuous supply of H2. Compared with the traditional UASB reactor (R1), the production of H2 was promoted in the bioelectrode–UASB coupled system (R2), and was consumed as an internal electron donor for p-ClNB reductive transformation by anaerobic microbes simultaneously. Furthermore, the cyclic voltammetry curve (CV) analysis of biocathodes showed a positive shift in the reductive peak potential and a dramatic increase in the reductive peak current, which demonstrated the catalytic reduction of p-ClNB by biocathode in the combined system.

Hydrogen production from alcohol wastewater with added fermentation residue by an anaerobic sequencing batch reactor (ASBR) under thermophilic operation

The objective of this study was to investigate the enhancement of hydrogen production from alcohol wastewater by adding fermentation residue using an anaerobic sequencing batch reactor (ASBR) under thermophillic operation (55 °C) and at a constant pH of 5.5. The digestibility of the added fermentation residue was also evaluated. For a first set of previous experiments, the ASBR system was operated to obtain an optimum COD loading rate of 50.6 kg/m3 d of alcohol wastewater without added fermentation residue and the produced gas contained 31% H2 and 69% CO2. In this experiment, the effect of added fermentation residue (100–1200 mg/l) on hydrogen production performance was investigated under a COD loading rate of 50.6 kg/m3 d of the alcohol wastewater. At a fermentation residue concentration of 1000 mg/l, the produced gas contained 40% H2 and 60% CO2 without methane and the system gave the highest hydrogen yield and specific hydrogen production rate of 128 ml/g COD removed and 2880 ml/l d, respectively. Under thermophilic operation with a high total COD loading rate (51.8 kg/m3 d) and a short HRT (21 h) at pH 5.5, the ASBR system could only break down cellulose (41.6%) and hemicellulose (21.8%), not decompose lignin.

Evaluation of Integrated Pollution Prevention Control in a textile fiber production and dyeing mill

Abstract Cleaner production assessment studies were conducted in a textile mill employing wool and acrylic fiber production and subsequent dyeing. A company-wide mass-balance analysis was performed. Various specific consumptions, emissions and waste generations were determined. The performance of the mill was evaluated based on BREF Documents. Water quality analysis indicated that process wastewaters from wool yarn softening, LP-VP printing machines and acrylic yarn washing could be reused in these processes, even without further treatment. Process wastewaters from wool yarn washing and softening in hank dyeing machines could be directly reused in tank washings and/or blended with process waters for direct reuse in the same or other processes. By the application of suggested BAT including wastewater reuse, machinery modifications, reuse of steam condensate, and good management practices, total water consumption may be reduced 35–65%. Substitution of 12 chemicals with more biodegradable and less toxic ones and installation of automatic chemical dosage systems may decrease COD loads about 25–50%. Furthermore, chemical and dyestuff consumptions could be reduced 31%. Energy consumption could be reduced by BAT suggestions including implementation of energy recovery systems for high temperature wastewater flows and flue gas emissions; process monitoring-control and various machinery optimization. Thus, potential reductions in total energy consumption in the mill may be up to 70%. Waste gas emissions could be reduced 25–65%. Waste generations may be decreased 5–10% with good management practices and reuse of especially textile wastes. Pay-back period of the suggested BAT options was found to be generally up to 4 years.

Application of intensified Fenton oxidation to the treatment of sawmill wastewater

The application of the Fenton process for the treatment of sawmill wastewater has been investigated. The sawmill wastewater was characterized by a moderate COD load (≈3gL−1), high ecotoxicity (≈40toxicity units) and almost negligible BOD/COD ratio (5×10−3) due to the presence of different fungicides such as propiconazole and 3-iodo-2-propynyl butyl carbamate, being the wastewater classified as non-biodegradable. The effect of the key Fenton variables (temperature (50–120°C), catalyst concentration (25–100mgL−1 Fe3+), H2O2 dose (1 and 2 times the stoichiometric dose) and the mode of H2O2 addition) on COD reduction and mineralization was investigated in order to fulfill the allowable local limits for industrial wastewater discharge and achieve an efficient consumption of H2O2 in short reaction times (1h). Increasing the temperature clearly improved the oxidation rate and mineralization degree, achieving 60% COD reduction and 50% mineralization at 120°C after 1h with the stoichiometric H2O2 dose and 25mgL−1 Fe3+. The distribution of H2O2 in multiple additions throughout the reaction time was clearly beneficial avoiding competitive scavenging reactions and thus, achieving higher efficiencies of H2O2 consumption (XCOD≈80%). The main by-products were non-toxic short-chain organic acids (acetic, oxalic and formic). Thus, the application of the Fenton process allowed reaching the local limits for industrial wastewater discharge into local sewer system at a relatively low cost.

Analysis of the time series of waste water quality at the inflow of the wastewater treatment plant and transfer functions

Abstract Time series of the daily total precipitation, daily wastewater discharges and daily concentrations and pollution loads of BOD5, COD, SS, N-NH4, Ntot and Ptot were analyzed at the inflow to the wastewater treatment plant (WWTP) for a larger city in 2004-2009 (WWTP is loaded by pollution from 435,000 equivalent inhabitants). The time series of the outflow from a WWTP was also available for 2007. The time series of daily total precipitation, daily wastewater discharges, concentrations and pollution loads at the inflow and outflow from the WWTP were standardized year by year to exclude a long-term trend, and periodic components with a period of 7 days and 365 days (and potentially also 186.5 days) were excluded from the standardized series. However, these two operations eliminated only a small part of the variance; there was a substantial reduction in the variance only for ammonium nitrogen and total nitrogen at the inflow and outflow from a WWTP. The relationship between the inflow into a WWTP and the outflow from a WWTP for the concentrations and pollution loads was described by simple transfer functions (SISO models) and more complicated transfer functions (MISO models). A simple transfer function (SISO model) was employed to describe the relationship between the daily total precipitation and the wastewater discharge.

Inhibition of the activities of activated sludge in a sequencing batch reactor by high-strength ammonium nitrogen

Two sequencing batch reactors were applied to investigate the activated sludge activities by high-concentration ammonia. The results indicated that the activity of nitrifying bacteria was much more susceptible than that of organics-utilizing bacteria and more severely inhibited by high-concentration ammonia. DHA in one SBR time cycle was increased to a maximum at first and then gradually decreased to a minimum value, which indicated that the activities of organics-utilizing bacteria could be maintained stably when fed with plenty of organic nutrients under high-concentration ammonia, but both the removed load of COD and NH4-N in activated sludge acclimated under high-concentration ammonia were higher than that under normal conditions, and the DHA declining rate of sludge acclimated under high-concentration ammonia was slower. This means that the activated sludge acclimated under high-concentration ammonia was also able to obtain strong resistance to inhibition by high-concentration ammonia, and the ratio of nitrifying bacteria to heterotrophic bacteria was increased gradually.

Pilot-scale nitrogen removal from leachate by ex situ nitrification and in situ denitrification in a landfill bioreactor

A combined process consisting of ex situ nitrification and in situ denitrification in landfill refuse was studied in pilot scale for nitrogen removal from municipal landfill leachate. The results showed that above 80% of partial nitrification ratio and an average COD loading rate of 1.50kgm−3d−1 were steadily maintained under DO concentrations of 1.0–1.7mgL−1 in the aerobic reactor. Quantitative PCR results indicated that nitrite-oxidizing bacteria being sensitive to DO fluctuations lead to partial nitrification when free ammonia inhibition was weak. Nitrified landfill leachate could be denitrified in the landfill bioreactor with maximum total oxidizing nitrogen removal rate of 67.2gNt−1TSwasted−1. Clone and sequencing analysis of denitrifying bacterial nirS gene inferred that heterotrophic denitrifier Azoarcus tolulyticu was the primary nitrogen converter in the landfill bioreactor. The obtained results will provide valuable information for optimizing the design and operation of a landfill bioreactor.

Efficacies of Various Inoculum Sources on Methane Production from Agro-industrial Wastewaters

One key factor in reactor start-up is inoculum seed. Normally, the indigenous seed is used; however, it is not available near the new biogas plant. The exogenous seed from different wastes treatment system should be considered. This study selected inoculum seeds and wastewaters from various agro-industrial wastewaters based on carbohydrate, lipid and protein manufacturers including a concentrated rubber factory (RB), cassava starch factory (CS), palm oil mill factory (PO), swine farm (SW) and soymilk processing factory (SM). A 5 x 5 inoculum seeds and a wastewaters factorial experimental design were investigated in batch operation mode at an organic loading of 2g COD l-1 and 37°C incubation. The results showed that all of the inoculum seeds can be used to degrade the exogenous wastewaters to methane. It was noted that the inoculum seeds can be applied to other sources of wastewater. The efficacy of inoculum seeds to start-up the anaerobic reactor depends on the initial activity and biodegradability of wastewater composition.

Removal of selected steroid estrogens in a sewage treatment plant with Unitank process in Nanjing, China

This study monitored estrone (E1), 17b-estradiol (E2) and 17a-ethynylestradiol (EE2) concentrations monthly for one year in the influent, effluent and various unit processes of a Unitank-based sewage treatment plant in Nanjing, China. The results showed that the concentrations of E1, E2 and EE2 in influents were 32.4–89.0 ng∙L–1, 19.4–78.0 ng∙L–1 and 12.3–45.0 ng∙L–1, respectively. Estrogen concentrations in influents were significantly higher in summer than those in winter. The removal efficiencies of E1, E2 and EE2 varied from 21.3 to 77.0%, 23.4 to 73.5%, and 25.2 to 68.1%, respectively, depending on seasonal variation. Biodegradation contributed more to the removal of estrogens than the grit chamber. Higher temperature and enhanced nitrifying activity appeared to be conducive to estrogens removal, and the influent COD loading should be less than 0.11 kg COD kg MLSS–1 d–1 to achieve optimal removal of estrogens.

Sludge bulking in a high-rate denitrifying automatic circulation (DAC) reactor

Sludge bulking and its effect on the performance of high-rate denitrifying automatic circulation reactor was studied in this paper. The results showed that, when the nitrogen loading rate and COD loading rate exceeded 65kgNm−3d−1 and 325kgCODm−3d−1, respectively, the nitrogen removal rate and COD removal rate decreased from 57.13kgNm−3d−1 and 232.57kgCODm−3d−1 to 38.08kgNm−3d−1 and 174.32kgCODm−3d−1, respectively. The performance of high-rate reactor deteriorated suddenly due to the insufficient biomass which originated from denitrifying sludge bulking and wash-out. The bulking denitrifying sludge was poor in settlement with the sludge volume index of 150.08±20.05mLg−1, and low in relative settling velocity ratio (average settling velocity to upflow velocity ratio) of 0.90±0.11. The denitrifying sludge bulking was identified as viscous bulking which was ascribed to the excessive production of extracellular polymers (EPS) (more than 450mggVSS−1) at the super high loading rate. The viscous bulking can be characterized by a noticeable decrease of bacteria/EPS ratio to 1.22±0.13 and a large increase of granule water content to 92.46±0.05%, which indicated that the bulking sludge lost its shape and approached its flow state.

Successful application of nitritation/anammox to wastewater with elevated organic carbon to ammonia ratios

The nitritation/anammox process has been mainly applied to high-strength nitrogenous wastewaters with very low biodegradable organic carbon content (<0.5 g COD∙g N−1). However, several wastewaters have biodegradable organic carbon to nitrogen (COD/N) ratios between 0.5 and 1.7 g COD∙g N−1 and thus, contain elevated amounts of organic carbon but not enough for heterotrophic denitrification. In this study, the influence of elevated COD/N ratios was studied on a nitritation/anammox process with suspended sludge. In a step-wise manner, the influent COD/N ratio was increased to 1.4 g COD∙g N−1 by supplementing digester supernatant with acetate. The increasing availability of COD led to an increase of the nitrogen removal efficiency from around 85% with pure digester supernatant to >95% with added acetate while the nitrogen elimination rate stayed constant (275 ± 40 mg N∙L−1∙d−1). Anammox activity and abundance of anammox bacteria (AMX) were strongly correlated, and with increasing influent COD/N ratio both decreased steadily. At the same time, heterotrophic denitrification with nitrite and the activity of ammonia oxidising bacteria (AOB) gradually increased. Simultaneously, the sludge retention time (SRT) decreased significantly with increasing COD loading to about 15 d and reached critical values for the slowly growing AMX. When the SRT was increased by reducing biomass loss with the effluent, AMX activity and abundance started to rise again, while the AOB activity remained unaltered. Fluorescent in-situ hybridisation (FISH) showed that the initial AMX community shifted within only 40 d from a mixed AMX community to “Candidatus Brocadia fulgida” as the dominant AMX type with an influent COD/N ratio of 0.8 g COD∙g N−1 and higher. “Ca. Brocadia fulgida” is known to oxidise acetate, and its ability to outcompete other types of AMX indicates that AMX participated in acetate oxidation. In a later phase, glucose was added to the influent instead of acetate. The new substrate composition did not significantly influence the nitrogen removal nor the AMX activity, and “Ca. Brocadia fulgida” remained the dominant type of AMX. Overall, this study showed that AMX can coexist with heterotrophic bacteria at elevated influent COD/N ratios if a sufficiently high SRT is maintained.