Influent Chemical Oxygen Demand Research Articles

Low-cost, reliable, and highly efficient removal of COD and total nitrogen from sewage using a sponge-filled trickling filter

ABSTRACT Development of low-cost and reliable reactors that need minimal supervision is a need-of-the-hour for sewage treatment in rural areas. This study explores the performance of a multi-stage sponge-filled trickling filter (SPTF) for sewage treatment, employing polyethylene (PE) and polyurethane (PU) media. Chemical oxygen demand (COD) and nitrogen removal/transformation were evaluated at hydraulic loading rates (HLRs) ranging from 2 to 6 m/d using synthetic sewage as an influent. At influent COD of ∼350 mg/L, PU-SPTF and PE-SPTF achieved a COD removal of 97% across all HLRs with most of the COD removal occurring in the first segments. Operation of PE-SPTF at an HLR of 6 m/d resulted in a substantial wash-out of biomass, while PU-SPTF retained biomass and achieved effluent COD < 10 mg/L even at an HLR of 8–10 m/d. The maximum total nitrogen (TN) removal by PE-SPTF and PU-SPTF reactors was 93.56 ± 1.36 and 92.24 ± 0.66%, respectively, at an HLR of 6 m/d. Simultaneous removal of ammonia (NH4-N) and nitrate (NO3-N) was observed at all the HLRs in the first segment of both SPTFs indicating ANAMMOX activity. The COD removal data, packed media depth, and HLRs were fitted (R2 > 0.99) to a first-order kinetic relationship. For a comparable COD removal, CO2 emission by PU-SPTF was 3.5% of that of an activated sludge system.

Ammonia recovery via stripping from hydrothermal liquefaction aqueous from sludge for anaerobic co-digestion pretreatment

Hydrothermal liquefaction (HTL) is a thermo-chemical method of processing wastewater solids that could be preferential over anaerobic digestion (AD) because it produces a greatly reduced volume of solids. Instead, the effluent can be separated into biocrude refined into fuel, hydrochar a high solid and HTL aqueous waste. Unfortunately, HTL aqueous is high in ammonia, phenolics, and nitrogen heterocyclic compounds that can inhibit AD if used for treatment. Ammonia stripping was tested for pretreatment of HTL aqueous from dewatered mixed sludge at 350 °C, 15 min and recovering ammonia. Seven stripping reactor conditions were run, and the best results were seen at 85 °C, a pH of 9.3 and 500 mL/min air flow rate. This case achieved ammonia and total phenolic compounds removal of 99.5 ± 0.1 and 32 ± 1 %, respectively, in 4 h. The ammonia stripping was coupled with acid adsorption to produce an ammonium sulphate salt with fertilizer value. The ideal ammonia stripping conditions produced a salt with a purity of 98.0 ± 0.05 % and represented an ammonia recovery of 73.9 ± 0.04 %. Semi-continuous flow bench-scale thermophilic anaerobic co-digestion of HTL aqueous with municipal sludge found that 12 % of influent chemical oxygen demand (COD) can come from HTL aqueous without inhibition if pretreated with ammonia stripping, while the digester fed with a similar COD from non-pretreated HTL aqueous showed inhibition. Under mesophilic conditions, semi-continuous flow anaerobic co-digestion was successful for non-pretreated and pretreated HTL aqueous even with 24 % and 22 % of influent COD provided by HTL aqueous, respectively.

Treatment of textile industry effluents with up‐flow anaerobic sulfidogenic reactor

AbstractBACKGROUNDDyes present in textile wastewater can pose various environmental problems, including toxicity, carcinogenicity and mutagenicity, when released into receiving environments. Sulfidogenic bacteria play a crucial role in wastewater treatment by reducing sulfate and producing sulfide through the utilization of organic compounds in water. The resulting sulfide often transfers its electrons to another electron acceptor. This study focused on the treatment of real textile wastewater using an up‐flow sulfidogenic column bioreactor.RESULTSThe reactor was acclimated to sulfate‐reducing conditions when influent chemical oxygen demand and sulfate concentrations were 1742 and 2000 mg L−1, respectively. Subsequently, a gradual transition was made from sulfate‐reducing conditions to dye‐reducing conditions. Throughout the study, the hydraulic retention time was maintained at 1 day.CONCLUSIONThe influent dye concentration was 2722 Pt‐Co, and an impressive dye removal efficiency of approximately 90 ± 2% was achieved. This corresponds to a removal rate of 2450 Pt‐Co L−1 day−1. Although the sulfide concentration in the reactor decreased in the last period, investigating the extent to which this sulfide participates in the dye removal may expand the use of sulfidogenic reactors in the treatment of real textile industry wastewater. © 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Effects of contact/stabilization time ratio on organic carbon-methane conversion in high-rate contact stabilization system

The high-rate contact stabilization (HRCS) process is a promising technique for recovering carbon from wastewater. However, its practical application faces challenges due to its low chemical oxygen demand (COD) removal efficiency, which requires further optimization. The objective of this study was to investigate the optimal process conditions for enhancing COD removal efficiency and carbon recovery rate (CRR) in the HRCS process. To achieve this, a sequencing batch reactor (SBR) was utilized to maximize the feast-famine regime. Although the HRCS process exhibited a lower COD removal efficiency compared to the high-rate activated sludge (HRAS) process in SBR mode, it demonstrated a 16.3 % higher CRR. The influence of the contact time to stabilization time (tc/ts ratio) on both COD removal efficiency and CRR was investigated. The optimum condition was achieved at a tc/ts ratio of 0.18, which resulted in a COD removal efficiency of 60.2 ± 3.0 % and a CRR of 0.417 ± 0.041 g-CODCH4/g-CODinf (CODCH4: produced methane as COD, CODinf: influent COD). The microbial communities in HRAS and HRCS exhibited simplification compared to conventional activated sludge. Distinct shifts were observed in response to changes in solids retention time and tc/ts ratio. Under harsher operating conditions, Lactococcus spp. became the predominant species, achieving the greatest dominance at a tc/ts ratio of 0.18. This is because they produce more extracellular polymeric substances and polyhydroxyalkanoates, which improve organic capture. The operating conditions identified in this study are anticipated to make a significant contribution to practical applications aimed at enhancing carbon recovery.

Achieving mainstream partial nitritation with aerobic granular sludge treating high-rate activated sludge effluent

New configurations for wastewater treatment plants (WWTPs) are under development to increase their self-sufficiency and sustainability. One is the A-B process, in which the A-stage is designed to maximize the redirection of influent chemical oxygen demand (COD) to the production of biogas. A promising A-stage alternative is the high-rate activated sludge (HRAS). B-stage, on the other hand, can consist of the combined partial nitritation (PN)-anaerobic ammonium oxidation (anammox). In this study, PN with aerobic granular sludge (AGS) was attempted under mainstream conditions at pilot scale. The effluent of a HRAS system – ideally operating at 2 g/L of total suspended solids, 0.5 mg/L of dissolved oxygen and 1 h of hydraulic retention time (52 ± 13 % COD removal) – was fed to the PN-AGS reactor initially inoculated with floccular sludge. Granulation and PN were studied with daily/seasonal fluctuations and without adding external reagents. Selective wasting from the top of the settled sludge bed was found a successful strategy to trigger granular sludge formation. The maintenance of a low sludge volume index (SVI < 100 mL/g) was helpful enough for improved operation of the system (i.e., COD removal and PN). Stable PN was achieved due to the suppression of the nitrite oxidizing bacteria activity by inhibitory levels of free nitrous acid. Finally, working with fast settling biomass at long settling times reduced the influent-biomass-nitrite contact and, thus, denitritation.

A nano-Al2O3 modified polypropylene hollow fiber membrane with enhanced biofilm formation in membrane aerated biofilm reactor application

Membrane Aerated Biofilm Reactor (MABR) stands out as an innovative technology for wastewater treatment. However, biofilm formation poses a significant challenge in its implementation. Surface modification emerges as a viable strategy to enhance biofilm development. In this study, biofilm formation was effectively promoted by coating polydopamine (PDA) and loading aluminum oxide nanoparticles (Al2O3 NPs) onto a polypropylene (PP) hollow fiber membrane, aiming to improve wettability and potential. Results from the bacterial attachment assay demonstrated a significantly higher bacterial attachment rate on the membrane loaded with Al2O3 NPs compared to PDA/PP and PP membranes. A comprehensive investigation into the MABR process was conducted, assessing both short-term and long-term (72 days) performance. In the short-term process, the Al2O3 NPs-PDA modified membrane exhibited superior removal efficiency for chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), and total nitrogen (TN) compared to other membranes. Transitioning to the long-term process, the start-up period for the Al2O3 NPs(10)-PDA/PP membrane was notably shortened to 27 days, surpassing the start-up times of PP and PDA/PP membranes by 13 and 5 days, respectively. Throughout the long-term operation, when the influent COD, NH4+-N, and TN concentrations increased, the Al2O3 NPs-PDA/PP membrane consistently maintained removal efficiency above 95%, 98%, and 85% for COD, NH4+-N, and TN, respectively, demonstrating excellent resistance to shock loading.

Analysis on Operation and Water Quality Characteristics of Centralized Wastewater Treatment Plants of Industrial Parks in Yellow River Basin, China

The Yellow River basin serves as an important economic belt and industrial base in China, featuring numerous industrial parks. However, alongside its economic significance, the basin struggles with significant water environmental challenges. This study analyzed the operational status, influent water quality, and energy consumption of 63 centralized wastewater treatment plants (WWTPs) from 54 major industrial parks in the Yellow River basin. The scale of these WWTPs was primarily within the range of 1 × 104~5 × 104 m3/d, with an average hydraulic loading rate of 53.8%. Aerobic treatment processes are predominant. The influent concentrations of chemical oxygen demand (COD), biochemical oxygen demand (BOD), ammonia nitrogen (NH3-N), total nitrogen (TN), and total phosphorus (TP) in the WWTPs exhibited a right-skewed distribution. The BOD/COD ratio of the WWTPs fluctuated between 0.1 and 1.6, and 75% of the WWTPs showed a COD/TN ratio lower than eight. The average BOD5/TN was 2.7, and the probability of influent BOD5/TP &gt; 20 was 84.6%. A significant linear correlation exists between the influent BOD and COD concentrations, while moderate linear relationships are also observed among NH3-N, TN and TP, emphasizing the importance of maintaining appropriate nitrogen and phosphorus levels for efficient pollutant removal. The average electricity consumption of WWTPs in the Yellow River basin in 2023 was 1.1 kWh/m3. It is important to upgrade these WWTPs and reduce their energy consumption. Further strengthening the construction of industrial wastewater collection and treatment facilities based on regional characteristics is recommended to promote the high-quality development of industrial wastewater treatment in the Yellow River basin.

Research and Development of the Treatment Effectiveness of a Novel Process for Vegetable Biogas Slurry Purification

Nowadays, an anaerobic filter is used in treating various wastewaters that is more effective for denitrification and organic removal. The Anaerobic Filter with Inoculum, Soft and Hard Packing Medium (AFISH) and Double-Filling Aerobic Baffle (DFAB) reactors were continuously operated for 120 days with a short Hydraulic Retention Time (HRT) in the range of 1 and 2 days at an Organic Loading Rate (OLR) of 0.58 and 1.08 gCOD/(l.d) by daily feeding the influent Chemical Oxygen Demand (COD) concentration between 1169 and 250 mg/l. After treating the sample wastewater in the new AFISH reactor, the effluent flowed into the DFAB reactor for further treatment to determine the treatment effectiveness of the novel AFISH and DFAB reactors at a short HRT of 1 to 2 days. The influent COD was reduced to 376 mg/l to 250 mg/l in a novel AFISH effluent and further dropped to 220 mg/l to 102 mg/l following DFAB reactor treatment. The COD removal in the AFISH reactor was around 67% when HRT was about 1 day, and a high COD value of 78% was removed during the HRT of 2 days, while in the DFAB reactor, the capability of treatment reached between 40% and 57% of the COD removed at the HRT of 1 and 2 days. The concentration of NH4-N in the effluent of the novel AFISH reactor was significantly lower than the effluent of the DFAB reactor, with NH4-N concentrations ranging from 157 mg/l to 330 mg/l. However, the treatment of vegetable bio-slurry from the Internal Circulation (IC) reactor by the novel AFISH and DFAB reactors satisfied the secondary wastewater discharge standard in the Integrated Wastewater Discharge Standard. Therefore, this novel process is one method beneficial for current and further research development that can be applied for industrial wastewater treatment processing and provides science information to those interested in research in the future.

Unveiling the power of COD/N on constructed wetlands in a short-term experiment: Exploring microbiota co-occurrence patterns and assembly dynamics

Constructed wetlands (CWs) are a cost-effective and environmentally friendly wastewater treatment technology. The influent chemical oxygen demand (COD)/nitrogen (N) ratio (CNR) plays a crucial role in microbial activity and purification performance. However, the effects of CNR changes on microbial diversity, interactions, and assembly processes in CWs are not well understood. In this study, we conducted comprehensive mechanistic experiments to investigate the response of CWs to changes in influent CNR, focusing on the effluent, rhizosphere, and substrate microbiota. Our goal is to provide new insights into CW management by integrating microbial ecology and environmental engineering perspectives. We constructed two groups of horizontal subsurface flow constructed wetlands (HFCWs) and set up three influent CNRs to analyse the microbial responses and nutrient removal. The results indicated that increasing influent CNR led to a decrease in microbial α-diversity and niche width. Genera involved in nitrogen removal and denitrification, such as Rhodobacter, Desulfovibrio, and Zoogloea, were enriched under medium/high CNR conditions, resulting in higher nitrate (NO3--N) removal (up to 99 %) than that under lower CNR conditions (<60 %). Environmental factors, including water temperature (WT), pH, and phosphorus (P), along with CNR-induced COD and NO3--N play important roles in microbial succession in HFCWs. The genus Nitrospira, which is involved in nitrification, exhibited a significant negative correlation (p < 0.05) with WT, COD, and P. Co-occurrence network analysis revealed that increasing influent CNR reduced the complexity of the network structure and increased microbial competition. Analysis using null models demonstrated that the microbial community assembly in HFCWs was primarily driven by stochastic processes under increasing influent CNR conditions. Furthermore, HFCWs with more stochastic microbial communities exhibited better denitrification performance (NO3--N removal). Overall, this study enhances our understanding of nutrient removal, microbial co-occurrence, and assembly mechanisms in CWs under varying influent CNRs.

Effects of Carbon Source on Denitrification and Electricity Generation in Composite Packing MFC-CW for Tail Water Treatment

The tail wastewater from sewage treatment facilities usually lacks carbon sources, and its subsequent treatment for deep nitrogen removal is difficult in natural conditions. In this study, the constructed wetland (CW) was integrated with microbial fuel cell (MFC) with high-density polyethylene (HDPE) fillers as the main matrix to improve nitrogen removal under inefficient carbon source conditions. Compared with the regular MFC and CW systems, MFC-CW attained higher nitrogen removal under low-carbon source conditions. The influence of influent carbon/nitrogen ratio (C/N) on the denitrification and electricity-generation performance was explored. Although the increase of carbon source simultaneously improved chemical oxygen demand (COD), ammonia (NH4+-N), nitrate (NO3−-N) and TN removal, the power generation during the carbon source adjustment showed low relation with the variation of influent COD in the range of 40–120 mg/L. CW was more dependent on carbon sources, and the addition of bioelectrochemical systems into MFC-CW could reduce the dependence of nitrogen removal on carbon sources, especially under low carbon source conditions. These findings offer valuable insights into the potential applications of MFC-CW for tail water treatment, and its parameters for utilization in real CWs should be explored in future studies.

Impact of waste separation on the biological nitrogen removal in a MSW incineration leachate treatment plant: Performance and microbial community shift

After waste separation program was launched in China in 2019, incineration leachate treatment plants are facing a challenge of effective removal of nitrogen from leachate due to lack of sufficient carbon source. In this study, the performance of a biological incineration leachate treatment process (anaerobic digestion (AD) - two-stage anoxic/aerobic (A/O) process) was evaluated after adopting the waste separation program, and the changes in the microbial community and function was analyzed using 16S rRNA amplicon sequencing technology. Results showed that after the waste separation, the influent chemical oxygen demand (COD) concentration reduced by 90% (from 19,300 to 1780 mg L−1) with the COD/N ratio decreased from 12.3 to 1.4, which led to a decreased nitrogen removal efficiency (NRE) of <65% and a high effluent NO3− accumulation (445.8–986.5 mg N·L−1). By bypassing approximately 60% of the influent to the two-stage A/O process and adding external carbon source (glucose), the mean NRE increased to 86.3 ± 7.4%. Spearman's analysis revealed that refractory compounds in the bypassed leachate were closely related to the variations in bacterial community composition and nitrogen removal function in the two-stage A/O, leading to a weakened correlation of microbial network. KEGG functional pathway predictions based on Tax4Fun also confirmed that the bypassed leachate induced xenobiotic compounds to the two-stage A/O process, the relative abundance of nitrogen metabolism was reduced by 32%, and more external carbon source was required to ensure the satisfactory nitrogen removal of >80%. The findings provide a good guide for regulation of incineration leachate treatment processes after the waste separation.

Uncovering interactions among ternary electron donors of organic carbon source, thiosulfate and Fe0 in mixotrophic advanced denitrification: Proof of concept from simulated to authentic secondary effluent

To offset the imperfections of higher cost and emission of CO2 greenhouse gas in heterotrophic denitrification (HDN) as well as longer start-up time in autotrophic denitrification (ADN), we synergized the potential ternary electron donors of organic carbon source, thiosulfate and zero-valent iron (Fe0) to achieve efficient mixotrophic denitrification (MDN) of oligotrophic secondary effluent. When the influent chemical oxygen demand to nitrogen (COD/N) ratio ascended gradually in the batch operation with sufficient sulfur to nitrogen (S/N) ratio, the MDN with thiosulfate and Fe0 added achieved the highest TN removal for treating simulated and authentic secondary effluents. The external carbon is imperative for initiating MDN, while thiosulfate is indispensable for promoting TN removal efficiency. Although Fe0 hardly donated electrons for denitrification, the suitable circumneutral environment for denitrification was implemented by OH− released from Fe0 corrosion, which neutralized H+generated during thiosulfate-driven ADN. Meanwhile, Fe0 corrosion consumed the dissolved oxygen (DO) and created the low DO environment suitable for anoxic denitrification. This process was further confirmed by the continuous flow operation for treating authentic secondary effluent. The TN removal efficiency achieved its maximum under the combination condition of influent COD/N ratio of 3.1–3.5 and S/N ratio of 2.0–2.1. Whether in batch or continuous flow operation, the coordination of thiosulfate and Fe0 maintained the dominance of Thiobacillus for ADN, with the dominant heterotrophic denitrifiers (e.g., Plasticicumulans, Terrimonas, Rhodanobacter and KD4–96) coexisting in MDN system. The interaction insights of ternary electron donors in MDN established a pathway for realizing high-efficiency nitrogen removal of secondary effluent.

Pilot study on ceramic flat membrane bioreactor in treatment of coal chemical wastewater

Some toxic and refractory pollutants in coal chemical wastewater can penetrate the biochemical treatment systems and cause high concentrations of suspended solids in the effluent, which may obstruct the subsequent advanced treatment. In this project, a submerged ceramic plate membrane system was integrated to the last oxic corridor of an existing multistage anoxic/oxic tank. In the ceramic flat membrane bioreactor, the influent chemical oxygen demand (COD) was 102.24–178.88 mg/L, with a removal ratio of approximately 30%. The NH3–N concentration in the effluent was relatively stable with an average value of 1.76 mg/L. The turbidity of the effluent was in the range of 0.235–0.852 NTU and was stable below 1 NTU. A flux of 30 L m−2·h−1 could meet the requirements of the pilot test. A gas-water ratio of 50:1 was found optimal. When the concentration of mixed liquor suspended solids (MLSS) was >3769 mg/L, the extracellular polymeric substance in the mixed solution was utilized by microorganisms as a substrate. High MLSS decreased membrane fouling rate. NaClO backwashing can effectively remove pollutants without adversely affecting the treatment efficiency of membrane bioreactors.

Application of Attached Growth System for Laundry Wastewater Treatment

Laundry wastewater can be treated in a small-scale aerobic wastewater treatment (WWT) system utilizing a microbubble generator (MBG). However, removing pollutants, precisely chemical oxygen demand (COD), is often low, especially under high wastewater load conditions. This study aims to improve the WWT system’s performance by incorporating an attached growth system. The research was conducted in a small-scale WWT system with a volume of 832 L in Cokrodiningratan, Code Riverbank, Yogyakarta, treating real wastewater from a nearby laundry shop. Experiments were performed batch-wise for one week with suspended and nylon-fabric-attached growth systems. Wastewater samples from the WWT system were taken and analyzed for COD concentrations. Results indicate that the attached growth system outperforms the suspended growth system. During operation, the suspended growth system achieved a COD removal rate of approximately 78% (temperature range of 26-28°C, a pH level of 6.3-7.1, and influent COD: 377.5 mg/L). In contrast, with the introduction of attachment media under similar batch operation conditions (temperature range: 26-28°C, pH level: 6.4-7.4, influent COD: 755.5 mg/L), the COD removal efficiency increased to 94%. The incorporation of attachment media led to a notably stable performance outcome.

Is constructed wetlands carbon source or carbon sink? Case analysis based on life cycle carbon emission accounting

Constructed wetlands (CWs) are widely used to polish the effluent of wastewater treatment plants and micro-polluted river or lake water. However, the impact of large-scale applications of CWs on carbon emissions is unclear. In this study, the carbon footprints of two full-scale hybrid CWs were determined based on life cycle assessment (LCA). Results showed that the carbon emission of CW ranged from 0.10 to 0.14 kg CO2-eq/m3, and was significantly correlated with the influent chemical oxygen demand loads and electricity consumption. However, CW would approach carbon neutrality during the service period when taking plant carbon sequestration into consideration. Compared with other advanced wastewater treatment technologies, CWs showed significant low-carbon emission and cost-effective benefits. This study clarified the role of CWs in the carbon cycle and would provide guidance for the construction and management of CWs.

Integration of Membrane Bioreactor and Reverse Osmosis for Textile Wastewater Treatment and Reclamation: A Pilot-Scale Study

Membrane bioreactor (MBR) technology, a combination of traditional activated sludge and membrane filtration, has been widely used for industrial wastewater treatment and reclamation. This paper highlights a pilot-scale MBR system treating textile wastewater from a textile factory in Taiwan. Over 7 months of continuous operation, the average MBR influent chemical oxygen demand (COD) is 332 mg/L, and the average effluent COD is 38 mg/L, which results in approximately 88% COD removal. A reverse osmosis (RO) module is installed after 2 months of MBR operation and uses the MBR permeate as its influent. The RO produces pure water with average COD, conductivity, and color of 7 mg/L, 16 μS/cm, and 7 Pt-Co, respectively. The RO permeate is suitable for reuse in manufacturing processes, and the RO membrane shows stable performance with TMP, which is less than or equal to 0.5 kg/cm2 during the test. The study demonstrates the great feasibility of MBR combined with RO for treating and reclaiming textile wastewater.

Enhanced Onsite Treatment of Domestic Wastewater Using an Integrated Settler-Based Biofilm Reactor with Efficient Biogas Generation

The growing population and increasing urbanization have led to a surge in domestic wastewater generation, posing significant challenges for effective and sustainable treatment. The present study demonstrates a novel and sustainable approach for the onsite treatment of domestic wastewater using an integrated settler-based biofilm reactor (ISBR) with efficient biogas generation. The ISBR provides an optimized environment for the growth of biofilm, facilitating the removal of organic pollutants and pathogens. Moreover, the ISBR enables the recovery of a valuable resource in the form of biogas, thus enhancing the overall utility of the treatment process. The performance of the ISBR was comprehensively evaluated at laboratory scale through treating the actual domestic wastewater generated from the hostel of Manipal University Jaipur. The ISBR system was operated under an ambient environment at a hydraulic retention time (HRT) of 24 h. The results demonstrated remarkable efficiency in terms of chemical oxygen demand (COD), total suspended solids (TSS), and coliforms removal, with average removal efficiency being more than 90%. According to the COD mass balance analysis, 48.2% of the influent COD was recovered as bioenergy. The chromatogram revealed a high percentage of methane gas in the collected biogas sample. The field emission scanning electron microscope (FESEM) analysis of the accumulated sludge in the ISBR system depicted the morphology of methanogenic bacteria. Both the experimental and theoretical results confirmed the feasibility and sustainability of the ISBR system at the onsite level.

Insights into greenhouse gas emissions from a wastewater treatment plant in vulnerable water areas of China

Wastewater treatment plants (WWTPs) are a significant anthropogenic source of greenhouse gas (GHG), but the quantitative assessment of GHG emissions from WWTPs in vulnerable water areas under stricter discharge limits remains unclear. Herein, depending on a case WWTP in southern China, we investigated the impacts of discharge standard improvement and key drivers of GHG emissions using daily operating data. We demonstrated that the stricter discharge limits increased the total GHG emission intensity by 18.2 %, with direct emissions increasing more than indirect GHG emissions. The GHG emissions were negatively correlated with water quantity, showing the scale effect, which became more pronounced after the discharge standard improvement. Increasing influent chemical oxygen demand and total nitrogen concentrations significantly drove the variations in GHG emissions, which were accelerated under stricter discharge limits. This study provides insights into the evaluation of GHG emission from WWTPs in vulnerable water areas and carbon-neutral wastewater management policies.

A novel long short-term memory artificial neural network (LSTM)-based soft-sensor to monitor and forecast wastewater treatment performance

Commercial instrumentation for measurement of various wastewater treatment processes parameters is costly and time-consuming in wastewater treatment plants (WWTPs). Long short-term memory neural network (LSTM) based soft-sensors to monitor and forecast crucial performance parameters including chemical oxygen demand (COD), NH4+ and total nitrogen (TN), which was based on lower-cost sensors dataset (e.g., dissolved oxygen, oxidation reduction potential (ORP) and suspended solids), were developed for a two-staged anoxic-oxic (A/O) process for wastewater treatment. Pearson correlation analysis was conducted to identify the essential model input features before LSTM development. With optimization of look-back periods, the proposed LSTM-based soft-sensors outperformed multiple linear regression model (MLR)-based soft-sensors for prediction of influent COD, influent NH4+, effluent COD and effluent TN. It was supported by the lower mean absolute percentage error, lower root mean squared error and higher Pearson correlation for LSTM-based soft-sensors compared to those of MLR-based soft-sensors. The overall results indicated that LSTM-based soft-sensors can achieve automated high-resolution measurement and effectively forecast the crucial performance of biological wastewater treatment, potentially lowering the capital cost for sensor installation in WWTPs.

Data-Based Modelling of Chemical Oxygen Demand for Industrial Wastewater Treatment

The aim of wastewater treatment plants (WWTPs) is to clean wastewater before it is discharged into the environment. Real-time monitoring and control will become more essential as the regulations for effluent discharges are likely to become stricter in the future. Model-based soft sensors provide a promising solution for estimating important process variables such as chemical oxygen demand (COD) and help in predicting the performance of WWTPs. This paper explores the possibility of using interpretable model structures for monitoring the influent and predicting the effluent of paper mill WWTPs by systematically finding the best model parameters using an exhaustive algorithm. Experimentation was conducted with regression models such as multiple linear regression (MLR) and partial least squares regression (PLSR), as well as LASSO regression with a nonlinear scaling function to account for nonlinearities. Some autoregressive time series models were also built. The results showed decent modelling accuracy when tested with test data acquired from a wastewater treatment process. The most notable test results included the autoregressive model with exogenous inputs for influent COD (correlation 0.89, mean absolute percentage error 8.1%) and a PLSR model for effluent COD prediction (correlation 0.77, mean absolute percentage error 7.6%) with 20 h prediction horizon. The results show that these models are accurate enough for real-time monitoring and prediction in an industrial WWTP.