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In this study, the effect of number of stages and bioreactor type on the removal performance of a sequential anaerobic-aerobic process employing activated sludge for the treatment of a simulated textile dyeing wastewater containing three commercial reactive azo dyes was considered. Two stage processes performed better than one stage ones, both in terms of overall organic and color removal, as well as the higher contribution of anaerobic stage to the overall removal performance, thereby making them a more energy efficient option. The employment of a moving bed sequencing batch biofilm reactor, which uses both suspended and attached biomass, for the implementation of the anaerobic stage of the process, was compared with a sequencing batch reactor that only employs suspended biomass. The results showed that, although there was no meaningful difference in biomass concentration between the two bioreactors, the latter reactor had better performance in terms of chemical oxygen demand (COD) removal efficiency and rate and color removal rate. Further exploratory tests revealed a difference between the roles of suspended and attached bacterial populations, with the former yielding better color removal whilst the latter had better COD removal performance. The sequential anaerobic-aerobic process, employing an aerobic membrane bioreactor in the aerobic stage resulted in COD and color removal of 77.1±7.9% and 79.9±1.5%, respectively. The incomplete COD and color removal was attributed to the presence of soluble microbial products in the effluent and the autoxidation of dye reduction metabolites, respectively. Also, aerobic partial mineralization of the dye reduction metabolites, was experimentally observed.

In recent years, research activities on water reuse applications have rapidly increased to manage natural water sources efficiently. Although these applications in centralized treatment systems can be effective, there are some drawbacks, including the economic factors for small settlements. In this study, a textile filtration unit with the integration of a sequencing batch reactor (SBR) was developed and different textile materials were used to enhance the treated effluent quality for reuse purposes. While the textile filtration unit alone could not effectively remove the pollutants, the removal efficiencies could not exceed 36% for COD and 50% for BOD5. However, SBR integration in to the filtration system improved the treated wastewater quality and COD and BOD5 reductions were obtained higher than 93%. Activated carbon coated cotton textile materials and activated carbon cloth, which was used for the first time for wastewater treatment, increased the treatment performance. In the filtration system, although the suspended solids were high in the SBR effluent, no clogging problem was observed even with higher operation times. This paper presents the research results on this textile filtration system, and experimental findings are discussed on the applicability of the system for small communities. HIGHLIGHTS Different textile cloths as low-cost materials were evaluated for wastewater treatment.; Activated carbon impregnated cotton textiles exhibited better treatment efficiencies.; Activated carbon cloth as an outer filtration material on the metal braided cotton textile showed remarkable reductions in all pollutants.; SBR integration enhanced the filtration unit performance.

The performance of a feedback control strategy in the operation of a sequencing batch reactor was evaluated. This strategy uses the online biogas flow measurements to define the duration of the reaction phase of each operating cycle, thereby increasing the energy production of the system and maximizing the methane production rate. The reaction phase is ended when the biogas flow rate reaches a sustained value significantly lower value than the maximum flow rate achieved, as a consequence of the depletion of the soluble chemical oxygen demand. The implementation of the depletion-time control was successful and reached a maximum methane production rate of 1.22 L CH4/d, showing an average productivity of 0.73 ± 0.3 L CH4/d. The reaction phase varied from 1.2 to 6 days with hydraulic retention times from 6 to 30 days. The use of this feedback control strategy increased the methane production and the energy production in 80% of the evaluated cycles (from 10.4 to 43.8%) compared to the operation of conventional AD without a control strategy. Furthermore, the strategy is easy to implement since it does not require complex calculations and uses a readily available biogas flow rate sensor. HIGHLIGHTS A control strategy to optimize methane production rate from organic solid waste was proposed.; The availability of the soluble substrate was an indicator to define the reaction time.; The implementation of the depletion-time control maximized the energy production rate.

Sequencing batch reactors (SBR) treating high-strength greywater need an aerobic granular sludge (AGS) with good properties, such as a low sludge volume index (SVI) and high settling velocities and substrate uptake rates to yield short settling and aeration stages. To promote the formation of stable granular sludge, the length of the famine phase could be a key factor. In this regard, the effect of the duration of this variable on the AGS properties was assessed by comparing a gradual versus an abrupt reduction of the famine phase in two SBR treating greywater. The initial average famine phase of 3.3 h was gradually reduced to 0.3 h over 20 weeks in one reactor, and abruptly in another one. This condition induced filamentous outgrowth, as well as the deterioration on the properties of the sludge; the effect was more accelerated when the famine periods were abruptly shortened. In both cases the reduction on the famine periods induced increased organic loading rates, which led to degranulation events when it was higher than 2.5 g-chemical oxygen demand g-volatile suspended solids−1 d−1. Afterwards, the biomass adapted to this situation, by forming new small-filamentous aggregates with similar SVI to that of the stable AGS formed with the longest famine period. HIGHLIGHTS The reduction in the famine phase length induces filamentous overgrowth and the deterioration of the properties of AGS.; Overstressed organic loading rates can lead to the biomass degranulation.; Small-size filamentous aggregates can present a similar sludge volume index to that of the stable-AGS.; A famine fraction of 0.55 with respect to the total cycle length is enough to ensure the stability of the AGS.

This study compares the H2 production from glucose, xylose, and acidic hydrolysates of Agave tequilana bagasse as substrates. The fermentation was performed in a granular sludge reactor operated in two phases: (1) model substrates (glucose and xylose) and (2) acidic hydrolysates at 35 °C, pH 4.5 and a hydraulic retention time of 5.5 h with glucose (10 g L−1) and xylose (12 g L−1). A sequencing batch reactor was used to acclimate the biomass between the glucose and xylose continuous fermentation (with a mixture of xylose-glucose) and acidic hydrolysates. During the discontinuous acclimating step, the xylose/glucose ratio increment negatively affected the H2 productivity. Although the continuous H2 production with xylose was negligible, the co-fermentation with glucose (88–12%) allowed H2 productivity of 2,889 ± 502 mL H2 L−1d−1. An acidic hydrolysate concentration of 3.3 gcarbohydrate L−1 showed a three-fold higher H2 productivity than with a concentration of 10 g L−1. The results indicated that xylose, as the only substrate, was challenging to metabolize by the inoculum, and its mixture with glucose improved the H2 productivity. Therefore, the low H2 productivity with hydrolysates could be related to the presence of xylose. HIGHLIGHTS The H2 productivities with glucose, xylose and acidic hydrolysates were contrasted.; H2 production was not observed with xylose as substrate in continuous operation.; H2 from acidic hydrolysates is affected by the xylose/glucose ratio and inhibitors.

Mezcal is an alcoholic artisanal drink made from agave plants in Mexico. Its production causes the generation of wastewater called vinasses, which are highly polluting residues due to its concentration of organic matter as chemical oxygen demand (COD) (35,000–122,000 mg/L) and acidity (pH < 4). Due to their organic content, these residues can be used in dark fermentation to obtain biogas, which is rich in hydrogen. In this work, the acclimation of inoculum by means of a dark fermentation process, in the presence of toxic compounds from mezcal vinasses was studied. The strategy of increasing the initial concentration of vinasse in each treatment cycle in a sequencing batch reactor (SBR) reactor was applied. It was possible to obtain a maximum biogas production of 984 ± 187 mL/L, from vinasses (18,367 ± 1,200 mg COD/L), with an organic matter removal efficiency of 20 ± 1%. A maximum generation of volatile fatty acids (VFA) of 980 ± 538 mg/L equivalent to a production of 74 ± 21% of the influent concentration and removal rate of organic matter of 1,125 ± 234 mg COD/L d−1 equivalent to a removal efficiency of 20 ± 4% was obtained from vinasses with a concentration of 19,648 ± 1,702 mg COD/L. HIGHLIGHTS Mezcal vinasses can be used as substrate for sustainable energy production.; Residues of mezcal production can be used in a dark fermentation to obtain biogas rich in hydrogen.; An efficient VFA production and maximum COD removal was obtained from an influent with 75% of mezcal vinasses.

This study aims at improving the existing algal-based wastewater treatment technologies by overcoming some of the major drawbacks of these systems such as large required land area, culture contamination, and energy-intensive algal harvesting. The experiments were carried out in an open photo-sequencing batch reactor at a laboratory-scale for nearly 2 months. A specific strain ACUS00207 of the aeroterrestrial green microalga Klebsormidium nitens (Kützing) Lokhorst was used. The strain is native to Bulgaria and belongs to a species that has never been used before in suspended growth systems for wastewater treatment for phosphorus removal. The culture of K. nitens showed promising results: phosphorus removal rates ranging from 0.4 to 1 mg total phosphorus L−1 d−1, efficient settling properties, and resistance to culture contamination with native microalgae. On the basis of the observed phosphorus removal mechanism of biologically mediated chemical precipitation/phosphorus precipitation, an innovative working mode of the sequencing batch reactor is suggested for reducing the hydraulic retention time and the required land area. HIGHLIGHTS Klebsormidium nitens used for the first time in suspended growth wastewater treatment.; Phosphorus removal rates ranging from 0.4 to 1 mg total phosphorus L−1 d−1.; Efficient settling properties and resistance to culture contamination.; Potential for reduction of the hydraulic retention time and the required land area.

[EN] According to previous research, it has been proved that wastewater treatment plants (WWTPs) can retain more than 90 % of the MPs contained in wastewater. However, a significant fraction of the MPs removed in WWTPs is retained in the sludge floc and this may lead to an environmental issue since biosolids can be used as fertilizers. The purpose of this research was to evaluate how the presence of polyethylene (PE) could interfere with the activated sludge performance. For this, a sequencing batch reactor (SBR) was continuously fed during 93 days with synthetic sewage and PE microbeads. It was observed that 98 +/- 2% of the total amount of MPs that entered SBR was accumulated in the activated sludge. Despite the high accumulation of MPs in the sludge, the depuration performance of the reactor was not compromised. However, the presence of MPs decreased the richness (Chao1) and abundance-based coverage estimators (ACE) and diversity (Shannon) of the bacterial community on day 93. Based on the analysis of the diversity indices and the relative abundances of microbial taxa, it was concluded that MPs had selective effects on activated sludge microbial community. However, MPs did not affect the abundance of nitrifying and denitrifying bacteria in the sludge., Authors thank the Spanish Ministry of Science, Innovation and Universities for the financial support (Reference of the project: RTI2018-096916-B-I00)

The current effluent standards emphasize on the removal of nutrients from sewage, and one solution is for establishments to install biological nutrient removal (BNR) technologies. However, there are several factors to be considered in installing or upgrading the technologies. Hence, the study utilizes two multi-criteria decision analysis (MCDA) tools to determine the important attributes and the optimal technology from the perspective of the academe, regulatory agency, and industry. Calibrated fuzzy analytical hierarchy process (FAHP) calculates the relative importance of the three criteria (implementability, financial, and socio-environmental) and twelve sub-criteria. On the other hand, the grey relational analysis is used to calculate the performance of the four selected alternatives: 3-stage Bardenpho (A2O), 5-stage Bardenpho (5BP), sequencing batch reactor (SBR), and membrane bioreactor (MBR). Combining the results of calibrated FAHP and GRA provided the overall ranking of alternatives. Results showed that each sector prioritized different factors in the selection of the optimal BNR technology. The academe considers socio-environmental (0.43) as the most preferred criterion, while the regulatory agency and industry consider financial (0.36) and implementability (0.57), respectively. Overall, the three sectors agreed that the sequential batch reactor (SBR) is the optimal BNR technology (GRG = 0.69 - 0.79).

Several water treatment techniques have been combined using the sequencing batch reactor with the membrane bioreactor for addressing water pollution. However, cleaning of the membrane is dependent on the approach involved as well as the operating conditions. In the present study, the sequencing-batch membrane bioreactor was used to treat real mixed municipal wastewater. The pollutant removal and membrane filtration performances were examined. The results show that the average removal rates of chemical oxygen demand (COD), total nitrogen, NH3-N, total phosphorus, and turbidity were 90.75, 63.52, 92.85, 87.58, and 99.48%, respectively, when the system was in continuous operation for 95 days. The membrane had a significant effect on COD and turbidity removal and provided stable performances for nitrogen and phosphorus removal. By observing the appearance of the membrane modules before and after the cleaning operation, it was concluded that the deposited sludge and granular sediment on the membrane surface can be effectively removed by hydraulic cleaning. In addition, recovery of membrane filtration performance to 60% of that of a new membrane can be achieved. Furthermore, we found that different sequences and duration of cleaning have different effects on the recovery of membrane filtration performance. HIGHLIGHTS Sequencing-batch membrane bioreactor (SMBR) was used to treat municipal wastewater.; We examined pollutant removal and membrane filtration performances over 95 days.; Removal rates of COD, TN, NH3-N, TP, and turbidity varied from 63.52 to 99.48%.; Recovery of membrane filtration performance to 60% was possible by hydraulic cleaning.; Recovery increases to 97.6% if alkaline and acid washes follow hydraulic cleaning.

The drinking water treatment plants (DWTPs) in the developing countries urgently need an efficient pre-treatment for nitrate (NO3−) removal to cope with the increasing NO3−pollution in raw water. An upflow sludge blanket (USB) reactor applied for NO3−removal from domestic wastewater may be adopted by the DWTPs. However, studies on the optimal carbon-to-nitrogen ratio (C/N) and operation of USB reactor at short hydraulic retention times (HRT) for high-rate polluted raw water pre-treatment are lacking. In this study, we first investigated the optimal C/N for biological NO3−removal in a sequencing batch reactor (SBR). An USB reactor was then operated with the optimal C/N for pre-treating synthetic raw water contaminated with NO3−(40 mg N L− 1) to monitor the NO3−removal performance and to examine opportunities for reducing the HRT. After operating the SBR with designed C/N of 4, 3 and 2 g C g− 1N, we selected C/N of 3 g C g− 1N as the optimal ratio due to the lower carbon breakthrough and nitrite (NO2−) accumulation in the SBR. The USB reactor achieved complete NO3−and NO2−removal with a lower designed C/N of 2 g C g− 1N due to the longer sludge retention time when compared with that of SBR (10 d). The high specific denitrification rate (18.7 ± 3.6 mg N g− 1mixed liquor volatile suspended solids h− 1) suggested a possible HRT reduction to 36 min. We successfully demonstrated an USB reactor for high-rate NO3−removal, which could be a promising technology for DWTPs to pre-treat raw water sources polluted with NO3−.

In this study, spent mushroom substrates (SMSs) were fermented anaerobically at room temperature to gain liquid SMSs (LSMSs) that were used to remove nitrogen from the piggery wastewater with a low C/N ratio in a sequencing batch reactor (SBR) and solid SMSs (SSMSs) that were utilized to adsorb Pb2+ from Pb2+-containing wastewater in a fixed-bed reactor (FBR). After LSMSs supplement, the removal efficiency of both total nitrogen (TN) and NH+4-N increased from around 50% to 60–80%. High-throughput sequencing results presented an obvious change in microbial diversity, and some functional microorganisms like Zoogloea and Hydrogenophaga predominated to promote nitrogen removal. Pb2+ did not emerge from the effluent until 240 min with the corresponding concentration being less than 3 mg/L when using 30-day SSMSs as adsorbents, and it was demonstrated to be appropriate to use the Thomas model to predict Pb2+ sorption on SSMSs. Although various functional groups played a role in binding ions, the carboxyl group was proved to contribute most to Pb2+ adsorption. These results certified that the anaerobically fermented SMSs are decidedly suitable for wastewater treatment. HIGHLIGHTS Anaerobically fermented spent mushroom substrates (AFSMS) could be recycled entirely.; AFSMSs were suitable for the treatment of piggery wastewater with a low C/N.; AFSMSs had a much higher capacity to adsorb Pb2+ than native SMSs.

The problem of effluent total nitrogen (TN) at most of the wastewater treatment plants (WWTPs) in China is important for meeting the related water quality standards, even under the condition of high energy consumption. To achieve better prediction and control of effluent TN concentration, an efficient prediction model, based on controllable operation parameters, was constructed in a sequencing batch reactor process. Compared with previous models, this model has two main characteristics: ① Superficial gas velocity and anoxic time are controllable operation parameters and are selected as the main input parameters instead of dissolved oxygen to improve the model controllability, and ② the model prediction accuracy is improved on the basis of a feedforward neural network (FFNN) with algorithm optimization. The results demonstrated that the FFNN model was efficiently optimized by scaled conjugate gradient, and the performance was excellent compared with other models in terms of the correlation coefficient (R). The optimized FFNN model could provide an accurate prediction of effluent TN based on influent water parameters and key control parameters. This study revealed the possible application of the optimized FFNN model for the efficient removal of pollutants and lower energy consumption at most of the WWTPs.

Perfluorooctane sulfonic acid (PFOS) has been widely detected in wastewater treatment plants (WWTPs). Here, we investigated the nitrogen removal efficiency of activated sludge and related stress mechanisms in a sequencing batch reactor (SBR) after 8 h exposure to PFOS at 10, 100, and 1000 μg L−1. At 10 μg L−1, no significant effect (p > 0.05) was observed on total nitrogen (TN) removal. However, the TN removal efficiency significantly increased from 79.24% (control) to 81.99% and 86.21% at high concentrations (100 and 1000 μg L−1), respectively. In addition, the activities of nitrogen removal enzymes such as ammonia monooxygenase, nitrite oxidoreductase, nitrate reductase, and nitrite reductase were promoted by PFOS, which had variation trends similar to the TN removal rates. High throughput sequencing revealed that acute-term exposure to PFOS had little influence on the microbial richness (Chao) and diversity (Shannon) of activated sludge, but the relative abundance of most nitrogen-removing bacteria increased (Paracoccus, Thauera, and Comamonas increased from 0.43%, 1.78%, and 1.52% in the control to 0.60%, 2.13%, and 1.74% in SBR3, respectively), which could explain the increased nitrogen removal efficiency. This might be due to the protection of relevant bacteria by extracellular polymeric substances (EPSs), because the EPS evidently increased at 100 and 1000 μg L−1. However, an extremely significant (p < 0.01) increase of reactive oxygen species production and lactate dehydrogenase release at 100 and 1000 μg L−1 PFOS showed that PFOS caused oxidative damage and destroyed the integrity of microbial cell membranes. This indicated that PFOS has an acute bio-augmentation effect on the nitrogen removal process in WWTPs, but causes cytotoxicity after acute exposure.

Mixed strains Delftia sp.YH01 and Acidovorax sp.YH02, with capability of heterotrophic nitrification-aerobic denitrification, were introduced into a two-stage aerobic sequencing batch reactor to enhance NO3−-N removal. With optimal C/N of 8, efficient NO3−-N removal was achieved at initial NO3−-N concentration of 2000 mg·L−1. Meanwhile, the massive accumulation of NO2−-N was avoided during the long operation. Compared to the one-stage aerobic sequencing batch reactor, the removal efficiency of NO3−-N and TN in the two-stage aerobic sequencing batch reactor was increased by 36.5% and 42.7%, which respectively was 93.8% and 88.4%. Microbial community study showed that the mixed strains have the stronger viability and can synergistically denitrify with the indigenous microorganisms in system, such as Azoarcus, Uncultured Saprospiraceae, Thauera, Paracocccus, which could be major contributors for aerobic denitrification. The proposed technology was shown to achieve high-efficiency treatment of high NO3−-N wastewater through aerobic denitrification.

The advanced biodegradation process of atrazine was stimulated with hydrogen peroxide (H(2)O(2)) in a sequencing batch reactor (SBR) under different operational conditions due to in situ generation of H(2)O(2)-peroxidase. The complete biodegradation and mineralization of 50 mg/L atrazine was achieved in the SBR with a biomass concentration of 328 mg/L stimulated with 10 mM of H(2)O(2). The presence of H(2)O(2) in the SBR induced the generation of H(2)O(2)-peroxidase resulted in acceleration of atrazine biodegradation. Adding moving media to the SBR system and converting it to the MSBR considerably improved the rate of atrazine biodegradation and mineralization under H(2)O(2) mediation. The highest specific utilization rate of atrazine in the SBR operated at the biomass concentration of 55 mg/L was 19.4 mg/g(biomass).h, while it was 33.5 mg/g(biomass).h in the MSBR operated at the biomass concentration of 37 mg/L. The low ATZ removal along with no peroxidase activity in the bioreactor in absence of H(2)O(2) clearly ideated that the biodegradation and mineralization of ATZ was considerably mediated by H(2)O(2)-peroxidase enzyme. The toxicity of atrazine solution decreased markedly when treated in the MSBR under optimum conditions. Accordingly, the MSBR stimulated with H(2)O(2) is an efficient and thus promising process for biodegradation of recalcitrant compounds.

Implementation of anaerobic ammonium oxidation (anammox) below its optimal temperature, known as “cold anammox”, may lead to its common use in wastewater treatment plants, reducing the operational costs of wastewater treatment. Thus, we investigated the effects of immobilization in polyvinyl alcohol–sodium alginate gel beads on anammox performance at temperatures of 30 °C, 23 °C, and 15 °C in laboratory-scale sequencing batch reactors. We determined the relative gene abundance of the nitrogen removal bacterial groups, which are considered as the key functional microbes of nitrogen cycle in activated sludge: denitrifies, ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and anammox bacteria. Nitrogen removal efficiency was higher for immobilized anammox sludge in comparison with non-immobilized anammox biomass at each investigated temperature. At 30 °C, nitrogen removal efficiency was 83.7 ± 6.46% for immobilized reactor, and 79.4 ± 7.83% for the control reactor, while at 15 °C was remained at the level of 50 ± 2.5% for immobilized reactor, and fluctuated from 13.2 to 45.3% for the control one. During temperature shifts, the process was also more stable in the case of the reactor with immobilized biomass. A statistically significant correlation was found between nitrogen removal efficiency and hydrazine oxidoreductase gene abundance.

Reducing the solids retention time (SRT) of the enhanced biological phosphorus removal (EBPR) process can increase organic carbon diversion to the sidestream for energy recovery, thereby realizing some of the benefits of the high rate activated sludge (HRAS) process. Determining the washout (i.e. minimum) SRT of polyphosphate accumulating organisms (PAOs), therefore, allows for simultaneous phosphorus and carbon diversion for energy recovery from EBPR systems. However, few studies have investigated the washout SRT of PAOs in real wastewater, and little is known of the diversity of PAOs in high rate EBPR systems. Here we demonstrate efficient phosphorus removal (83% orthophosphate removal) in a high rate EBPR sequencing batch reactor fed real primary effluent and operated at 20 °C. Stable operation was achieved at a total SRT of 1.8 ± 0.2 days and hydraulic retention time of 3.7–4.8 hours. 16S rRNA gene sequencing data demonstrated that Accumulibacter were the dominant PAO throughout the study, with a washout aerobic SRT between 0.8 and 1.4 days. qPCR targeting the polyphosphate kinase gene revealed that Accumulibacter clades IIA, IIB and IID dominated the PAO community at low SRT operation, while clade IA was washed out at the lowest SRT values.

Triclosan (TCS) is commonly found in wastewater treatment plants, which often affects biological treatment processes. The responses of nitrification, antibiotic resistome and microbial community under different TCS concentrations in activated sludge system were evaluated in this study. The experiment was conducted in a sequencing batch reactor (SBR) for 240 days. Quantitative PCR results demonstrated that the abundance of ammonium oxidizing bacteria could be temporarily inhibited by 1 mg/L TCS and then gradually recovered. And the abundances of nitrite oxidizing bacteria (NOB) under 2.5 and 4 mg/L TCS were three orders of magnitude lower than that of seed sludge, which accounted for partial nitrification. When the addition of TCS was stopped, the abundance of NOB increased. The mass balance experiments of TCS demonstrated that the primary removal pathway of TCS changed from adsorption to biodegradation as TCS was continuously added into the SBR system. Moreover, TCS increased the abundance of mexB, indicating the efflux pump might be the main TCS-resistance mechanism. As a response to TCS, bacteria could secrete more protein (PN) than polysaccharide. Three-dimensional excitation-emission matrix revealed that tryptophan PN-like substances might be the main component in PN to resist TCS. High-throughput sequencing found that the relative abundances of Paracoccus, Pseudoxanthomonas and Thauera increased, which could secrete extracellular polymeric substances (EPS). And Sphingopyxis might be the main TCS-degrading bacteria. Overall, TCS could cause partial nitrification and increase the relative abundances of EPS-secreting bacteria and TCS-degrading bacteria.

Leachate of the uncontrolled landfill contains pollutants, which is discharged directly into the environment. The main objective of this study is to evaluate the reduction of bacteriological and parasitological risks by four biological treatments: sequencing batch reactor, anaerobic, intensive aeration and combination of the three processes. The results showed high bacteriological pollution in the raw leachate: 1.12 × 107 CFU/ml, 6.7 × 106 and 5.26 × 104 for total coliforms, faecal coliforms and Streptococci, respectively, parasites of intestinal helminths are also present: 11.86, 9.49, 9.83, 8.81 eggs/L for Enterobius vermicularis, Ascaris lumbricoides, Trichuris and Hymenolepis nana, and the values are higher than the standards for discharge into the natural environment. After sequencing batch reactor treatment, a decrease is noted in bacteria, Staphylococci, total coliforms and Streptococci with 99.63%, 97.11%, 99.93% and 94.62% abatement, respectively. This process also removes 75% of total unviable form and 80% of viable form of parasites. Intensive aeration and anaerobic treatments allowed the total elimination of total coliforms. Anaerobic processing allowed a reduction of 33.4% of unviable forms and 37% of viable forms of parasites, while a reduction of 63% of unviable and 77% of viable parasites was reported by intensive aeration. The combined treatment improves the results with abatement rates to 100% for total coliforms bacteria, and viable forms of the genus parasites: Capillaria sp., Toxocara (nematodes), Hymenolepis nana and Taenia (cestodes). A principal component analysis showed very significant correlations between all measured variables (bacteria and parasites). Combined treatment appears to be the best treatment to reduce biological risks of leachate.

A sequencing batch reactor was constructed to realize simultaneous nitrification and denitrification (SND) and denitrifying phosphorus removal (DPR). The influence of different carbon sourc...

Meat factory effluent contains fat, protein, diluted blood, and suspended solids. As a result, nutrient and organic concentrations in this effluent are incredibly high, and residues are slightly solubilized, likely to impact environmental pollution on streams, rivers, and other watercourses if discharged untreated. The biodegradation of abattoir waste was studied using a laboratory-scale cylindrical sequencing batch reactor (SBR) in aerobic mode. The aerobic sludge was collected from the aeration compartment of a paper and pulp effluent treatment facility and cultivated in a 2.83-L Perspex-based laboratory SBR. The raw wastewater comprised 6494 ± 2144 mg/l chemical oxygen demand (COD), 1946 ± 607 mg/l biochemical oxygen demand (BOD), 1722 ± 159 mg/l total suspended solids (TSS), 3062 ± 592 mg/l CaCO3 alkalinity, 7.00 ± 0.27 pH. The duration of a complete cycle was 24 h and comprised four phases: fill (5 min), react (23 h 10 min), settle (40 min) and draw (5 min). The whole experiment was divided into four phases and the dilution was done with the help of domestic sewage. In the first stage, the reactor was fed four times diluted slaughterhouse effluent on a 24-h cyclic operation for two weeks. After achieving a significant reduction in COD, the organic content of the input was raised by lowering the dilution factor. In the second and third phases, the reactor was fed three times and twice diluted samples for two weeks each operating at the same cyclic interval. In the final stage, raw effluent was fed to the reactor for two more weeks. The average COD value of diluted wastewater in the first, second, third and fourth phase was 1040 mg/l, 3168 mg/l, 4800 mg/l, and 5200 mg/l, respectively. The COD removal efficiency at the end of the first, second, third and fourth phase was 83%, 93%, 85% and 97%, respectively. The average BOD value of diluted wastewater at the end of the first, second, third and fourth phase was 1120 mg/l, 610 mg/l, 1502 mg/l, and 1350 mg/l, respectively. The BOD removal efficiency at the end of the first, second, third and fourth phase was 84%, 88%, 85% and 98%, respectively. After 8 weeks, at an organic loading rate of 3.06 kg/m3/d, the final phase has achieved BOD and COD removal efficiency of 98% and 97%, respectively. The pH and alkalinity levels were within acceptable ranges. After two months, the sludge's settling characteristics have improved, and the nitrification efficiency of the reactor was roughly 60% at the time of deactivation of the reactor.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA transmission route was thoroughly investigated in the hospital wastewater, sewage collection network, and wastewater treatment plants. Samples were taken on four occasions from December 2020 to April 2021. The performance of two different wastewater treatment processes of sequencing batch reactor (SBR) and conventional activated sludge (CAS) was studied for virus destruction. For this purpose, liquid phase, solid phase and bioaerosol samples were taken from different units of the investigated wastewater treatment plants (WWTPs). The results revealed that all untreated hospital wastewater samples were positive for SARS-CoV-2 RNA. The virus detection frequency increased when the number of hospitalized cases increased. Detection of viral RNA in the wastewater collection system exhibited higher load of virus in the generated wastewater in areas with poor socioeconomic conditions. Virus detection in the emitted bioaerosols in WWTPs showed that bioaerosols released from CAS with surface aeration contains SARS-CoV-2 RNA posing a potential threat to the working staff of the WWTPs. However, no viral RNA was detected in the bioaerosols of the SBR with diffused aeration system. Investigation of SARS-CoV-2 RNA in WWTPs showed high affinity of the virus to be accumulated in biosolids rather than transporting via liquid phase. Following the fate of virus in sludge revealed that it is completely destructed in anaerobic sludge treatment process. Therefore, based on the results of the present study, it can be concluded that receiving water resources could not be contaminated with virus, if the wastewater treatment processes work properly., Graphical abstract Unlabelled Image

Intermittent cycle extended aeration system is a modification of a conventional sequencing batch reactor system in which the system is operated under continuous feed. The objective of this research is to study the effect of sludge retention time and aeration pattern on the performance of intermittent cycle extended aeration system pilot scale for wastewater treatment. In addition, the process simulation using GPS-X software was conducted. Five different runs of sludge retention times of 10, 15, 20, 25 and 30 days were studied. The optimum sludge retention time for wastewater treatment by intermittent cycle extended aeration system pilot scale was 10 days, and under operating condition of sludge retention time of 10 days, effluent quality was 15.5 ± 3.8, 6.5 ± 1.1, 5.3 ± 1.6, 0.7 ± 0.2, 5.0 ± 1.4 mg/L and 1.4 ± 0.7 mg/L for COD, BOD5, TSS, NH4–N, TN and TP which amply met the local regulation of class A treated wastewater. GPS-X sensitivity analysis tool box was used to determine the most sensitive kinetic parameters affecting the intermittent cycle extended aeration system pilot scale performance. Out of about 50 kinetic parameters, YH, bH, μA, Ko, bA, Ka and μPAO appeared to the most sensitive kinetic parameters. The calibrated GPS-X model proved that the presence of anoxic phase in the cycle has a significant impact on nitrogen and phosphorus removal. In addition, intermittent aeration pattern achieved the highest performance compared with other patterns of aeration only, aeration/anoxic and anoxic/aeration.

While enhanced biological phosphorus removal (EBPR) is widely utilized for phosphorus (P) removal from wastewater, understanding of efficient process alternatives that allow combined biological P removal and shortcut nitrogen (N) removal, such as nitritation–denitritation, is limited. Here, we demonstrate efficient and reliable combined total N, P, and chemical oxygen demand removal (70%, 83%, and 81%, respectively) in a sequencing batch reactor (SBR) treating real mainstream wastewater (primary effluent) at 20 °C. Anaerobic – aerobic cycling (with intermittent oxic/anoxic periods during aeration) was used to achieve consistent removal rates, nitrite oxidizing organism (NOO) suppression, and high effluent quality. Importantly, high resolution process monitoring coupled to ex situ batch activity assays demonstrated that robust biological P removal was coupled to energy and carbon efficient nitritation–denitritation, not simultaneous nitrification–denitrification, for the last >400 days of 531 total days of operation. Nitrous oxide emissions of 2.2% relative to the influent TKN (or 5.2% relative to total inorganic nitrogen removal) were similar to those measured in other shortcut N bioprocesses. No exogenous chemicals were needed to achieve consistent process stability and high removal rates in the face of frequent wet weather flows and highly variable influent concentrations. Process modeling reproduced the performance observed in the SBR and confirmed that nitrite drawdown via denitritation contributed to suppression of NOO activity.

Aerobic granular sludge (AGS) process is a fast-growing sustainable biological treatment for wastewater. Activated sludge (AS) is the standard inoculum used for cultivating AGS, even for the treatment of saline wastewaters. However, the application of the allochthonous AS community for both developing halotolerant AGS and establishing biological nutrient removal (BNR) under saline conditions is a challenging task. To circumvent this problem, herein, the cultivation of AGS directly from the autochthonous planktonic bacterial community of seawater was investigated. For developing halophilic AGS, a sequencing batch reactor was operated by directly supplying nutrient-amended seawater without inoculum (i.e., AS or AGS). The approach described herein succeeded in rapidly granulating the planktonic bacteria of seawater and establishing BNR at a 34 ppt salinity. The ammonium and total nitrogen removals of 92–100% and 81–90% were observed during 22–100 days of start-up, respectively. Interestingly, nitrite accumulation was not observed under saline conditions. Phosphate removal progressively improved and stabilized at over 76% within 2 months of start-up. The phosphate removal profiles comprised of P release and uptake phases, which are typical to those of the enhanced biological phosphorus removal mechanism. The granulation of planktonic microbes involved distinct events such as the formation of micro-aggregates, macro-aggregates, and granules but not flocs. Granular growth was observed within few days, suggesting that the granulation of the autochthonous planktonic microbial community of seawater is a rapid phenomenon. The granules were dense (1.5 g ml−1) and compact (SVI5: 6 ml g−1) and had an excellent settling velocity (41.2 m h−1) on day 25. Moreover, 16S rRNA gene sequencing revealed that AGS had lesser bacterial diversity than the seawater microbiome due to the enrichment of α-proteobacteria. The removal of nitrogen and phosphorus was not significantly impacted at the lower salinities of 25 and 17 ppt. Furthermore, the halophilic AGS was able to achieve an efficient BNR and treatment of real seafood processing wastewater without acclimation. Thus, granulation of the autochthonous halophilic bacteria of seawater is a novel strategy for developing halophilic AGS and to achieve a high BNR under saline conditions.

Industrial wastewater usually has high organic load and contain lots of toxic substances, which is hard to be treated. Because of many advantages such as the high organic loading rating tolerance, ...

Denitrifying polyphosphate accumulating organisms (DPAOs) are capable of nitrate (NO3−) and/or nitrite (NO2−) reduction coupled to phosphorus (P) uptake when subjected to alternating anaerobic/anoxic conditions. However, accumulation of the denitrification intermediate nitrous oxide (N2O), a potent greenhouse gas, has been previously observed in DPAO enrichments. To date, denitrification capability and denitrifying P uptake rates of DPAOs using different electron acceptors (NO3−, NO2−, and N2O) after long-term exposure and adaptation to elevated concentrations of NO2− characteristic of shortcut N removal systems have not been examined. To address this knowledge gap, we operated a lab-scale sequencing batch reactor under alternating anaerobic/anoxic conditions with high NO2− feed for over a year to obtain an enrichment of “Candidatus Accumulibacter phosphatis” capable of denitrifying P uptake. Ex situ batch assays were performed to clarify capacity for reduction of various nitrogen oxides and simultaneous P uptake by the DPAO enrichment culture under both decoupled (internal COD as electron donor) and coupled (external COD as electron donor) feeding conditions. These batch assays revealed distinct nitrogen oxides reduction and denitrifying P uptake capabilities, with significantly elevated kinetics when NO2− was supplied as the electron acceptor for P uptake. Surprisingly, N2O reduction was extremely slow when only internal storage polymers were present as an electron donor (decoupled feeding), as is typical for PAOs in practical enhanced biological P removal processes. This pattern held when N2O was the sole electron acceptor supplied, and when N2O was supplied with NO3− or NO2−. We documented a particularly strong propensity for N2O accumulation in the presence of NO2− under both decoupled and coupled scenarios. The formation of granular microbial aggregates in the reactor was observed without intentional granule selection. High-throughput 16S rRNA gene sequencing revealed selective enrichment of putative DPAOs in large granular biomass. qPCR-based profiling of denitrification functional genes demonstrated that smaller floccular aggregates had higher genomic potential for N2O production, while large granular aggregates likely played a role as a putative sink for N2O.

Lany landfill, located in the Czech Republic, generates around 10 m3/d of leachate, heavily polluted with ammoniacal nitrogen, heavy metals and salts, which needs to be treated onsite in order to minimize their effect on the ecosystem and on human health. A sequencing batch reactor (SBR) was designed for ammoniacal nitrogen removal from the leachate and the economic feasibility and environmental impact of the designed SBR was assessed. From the cost-benefit analysis, capital expenditure (CAPEX) of 33,500 €/year and operational expenditure (OPEX) of 13,521 €/year were estimated. A shadow price concept tool was used to calculate the environmental benefit as 21,000 €/year. The net present value of the project was evaluated to be 19,528 € with an internal rate of return of 21.6%. For environmental assessment, triple bottom line (TBL) analysis on the existing practice of discharging the leachate to a nearby wastewater treatment plant and on-site treatment using SBR was performed. The total score for existing practice was calculated to be 55.1% while for on-site treatment it was 59.6%. Based on the results it was concluded that on-site treatment is both economically and environmentally feasible. A mitigation plan was also prepared for the impacts identified in the environmental assessment.

A nitrogen removal system integrating partial nitrification, anaerobic ammonium oxidation (Anammox) and endogenous denitrification (PAED) was established in a sequencing batch reactor (SBR) for treating low nitrogen sewage (approximately 40 mg L−1 ammonia-nitrogen). The impact of sulfate on PAED sludge was investigated in five identical SBRs, fed with different levels of sulfate (0, 50, 100, 200 and 400 mg L−1). Ammonia oxidation was improved by the addition of Results showed that the sulfate addition in low concentration of sulfate (≤50 mg L−1), but was profoundly suppressed by higher levels of sulfate. Sulfate feeding enhanced both total nitrogen removal by Anammox and endogenous denitrification, with the abundance of Candidatus Kuenenia increasing to 4.39% in 400 mg L−1 sulfate from 0.83% in the control reactor, and Denitratisoma increasing to 6.35% from 2.77%. The results proved the feasibility of the PAED system in treating low nitrogen sewage with sulfate, which also enhanced the nitrogen-sulfate interaction.

The objective of the study was to explore the impact of different operation strategies on the performance of the Oxic-Settling-Anaerobic (OSA) process. A sequencing batch reactor was selected as the aerobic (oxic) unit of the OSA system and it was operated as a dual mixing phase with step feeding in order to optimize simultaneous nitrogen removal and sludge minimization. For this purpose, the effect of COD/N ratio, filling pattern and the fraction of anaerobic period was investigated on the performance of a laboratory-scale OSA system fed with synthetic wastewater (peptone mixture) approximating the characteristics of sewage. In nine consecutive experimental stages, each sustaining different metabolic processes and biochemical reactions, the sludge reduction potential of the OSA system was not impaired, maintaining an average observed yield value of 0.18 g VSS/g COD, which was approximately half the level observed in the reference reactor. Similarly, the OSA scheme of operation did not affect or alter the fundamental mechanisms of biological nitrogen removal, where system performance could be modified and optimized the same way as in a conventional activated sludge configuration. Furthermore, the OSA system maintained a higher level of biomass concentration compared with the reference reactor. This observation confirmed the previous analyses that the continuous biomass inflow from the side-stream anaerobic bioreactor was the reason to establish the microbial mechanism that resulted in a much lower sludge generation, regardless of the biochemical processes taking place in the reactor.

A partial nitritation (PN)/anaerobic ammonium oxidation (ANAMMOX) process in sequencing batch reactor (SBR) was successfully developed to treat high-strength ammonium wastewater. The feed distribution in the SBR cycle and sub-cycles was considered as the main operating strategy, and was optimized using a response surface methodology (RSM)-based optimization technique. In the SBR cycle, the maximum nitrogen removal rate (NRR) of 0.79 ± 0.01 kg m−3 d−1 was achieved by applying a feed distribution strategy that considered the kinetic characteristics of ANAMMOX and ammonia oxidizing bacteria (AOB). However, this strategy negatively affected the nitrogen removal efficiency (NRE) due to alkalinity loss. Therefore, the feed distribution in the SBR sub-cycles with respect to the NRE and the NRR was further studied. The nitrogen removal performance was optimized in the optimum region and an NRE of 88% and an NRR of 0.84 kg m−3 d−1 were achieved. The optimized model was verified in confirmation test. The RSM-based optimization results provide insights into the feed distribution strategy for achieving single-stage PN/ANAMMOX SBR operation.

In this work, the parametric optimization of real domestic wastewater treated in an activated sludge sequencing batch reactor (SBR) was performed by means of the response surface methodology (RSM). The influences of influent organic matter concentration as chemical oxygen demand (COD

Ibuprofen (IBU) containing wastewater with a concentration of 1-5 mg/L was treated in an activated sludge sequencing batch reactor (SBR), for 60 days, in order to investigate the overall performance of the SBR, the parameter variations during a typical cycle, the chemical composition and content of extracellular polymeric substances (EPS) and the evolution of microbial community. The average removal efficiencies of COD, NH4+-N and TN were >85%, while >40% of the IBU was removed and the removal efficiencies of TP fluctuated around ~ 75%. The EPS content increased significantly with IBU addition (p < 0.01). Fulvic acid-like substances in the chemical composition of EPS increased during the stable operation phase. Proteobacteria associated with nitrogen removal was the dominant phylum, which can also resist IBU stress. For the denitrifying bacteria, the OTUs of both Rhodobacter and Pseudomonas increased from day 1-30 and reduced on day 60 (p < 0.01), which was opposite to the results observed for Rhodocyclaceae (phosphorus-accumulating bacteria). The OTUs of Acidovorax showed an increasing trend (p < 0.01), whereas the OTUs for Nitrospira (nitrite oxidizers) and Nitrosomonas (ammonia oxidizers) decreased significantly (p < 0.05).

As a solution of the sludge loss in the treatment of saline wastewater, the granulation of halophilic sludge was explored in this study. The inoculated estuarine sediment was granulated to an average diameter of 1155 ± 102 μm under the selective settling pressure in the airlift sequencing batch reactor (SBR) when the influent organic loading rate (OLR) was doubled to 0.36 g COD/L·day. The results indicated that the OLR doubled the amount of total extracellular polymeric substance (EPS) and that protein was predominant in the EPS (72.8 ± 2.0%). The correlation between aggregate size and protein content was better than that between aggregate size and polysaccharide content. The amount of alginate-like exopolysaccharides (ALE) increased linearly at the mature granular stage, co-occurring with the compact and elastic structure of the granules. According to the results of 16S rRNA high -throughput sequencing, the Shannon-Weaver index of mature granule decreased by >50% compared to the inoculated sediment. Bacteria of Propionibacteriaceae family constituted 34% of the population in granules and were in symbiotic relationship with halophiles of family Rhodocyclaceae, Vibrionaceae, Flavobacteriaceae, and Cryomorphaceae. The aerobic halophilic granular sludge showed COD removal efficiency of 90.9 ± 0.8% and ammonia removal efficiency of 72.6 ± 4.0% for 30 g/L saline wastewater. An average nitrite accumulation ratio of 94.5 ± 2.9% was observed during nitrification. Granulation of halophilic sludge provides an effective solution to the saline sludge loss problem, which is a step forward to realize the biological treatment of saline wastewater by halophiles.

Drugs of addiction, have been recognized as potential contaminants of concern to the environment. Effluent wastewater discharge is a major source of contamination to aquatic receiving environments. A year-long monitoring program was undertaken in Australia to characterise the fate of four emerging drugs of addiction: methamphetamine; MDMA; pharmaceutical opioids: codeine and morphine and a metabolite: benzoylecgonine in four wastewater treatment plants operating with different secondary treatment technologies: conventional activated sludge (CAS), membrane bioreactors (MBR), integrated fixed-film AS (IFAS)and sequencing batch reactor (SBR). The effect of subsequent tertiary treatment (coagulation/flocculation)on the removal efficiency was also assessed. Drugs were detected in influent and effluent samples (mean concentration ranged from 43–4777 and 17–1721 ng/L, respectively). Treated effluents had noticeably lower levels compared to raw influents. Removal efficiency of compounds depended on the secondary treatment employed, with IFAS and MBR performing the best with significant removal of compounds (≈90%)followed by CAS (54–96%)and lastly SBR (42–83%). Despite the low levels of drugs measured after the secondary treatment, near complete removal after tertiary treatment (≈99%)was recorded, which demonstrated the effectiveness of using the coagulation/flocculation process as an effective step for enhancing the removal efficiency. The levels of drugs were at a low level in the effluents released into the environment and used for recycling and all posed a low environmental risk in urban water courses based on the risk assessment. The information given here provides new and useful information to the water industry and regulators on the efficiency of drug removal in a range of wastewater treatment configurations. Refereed/Peer-reviewed

The wood industry consumes a lot of water. Due to the reduction of water resources in the world, the treatment of this contaminated water is very essential. In this study, the removal efficiencies of the chemical oxygen demand (COD) and turbidity from woodchips wastewater with the use of a sequencing batch reactor (SBR) were studied at a bench scale. Woodchips wastewater samples were collected with a COD of 1300 mg L−1 and a turbidity of 93 NTU. The optimization of the SBR process was investigated by response surface methodology (RSM) based on a central composite design (CCD). A quadratic polynomial model was fit to the data with R2 of 0.9919 for COD reduction, R2 of 0.9910 for turbidity removal, and R2 of 0.9945 for sludge volume Index (SVI), respectively. The effect of three parameters, including initial COD, mixed liquor suspended solids (MLSS), and Hydraulic retention time (HRT) on the COD reduction and turbidity removal were evaluated. The initial COD (A), MLSS (B), cycle time (C), AB, AC, BC, A2, B2, and C2 were considered as the affective parameters in the COD reduction. Initial COD (A), MLSS (B), A2, B2, C2, AC, and BC were observed as the remarkable model terms on the turbidity removal. Also, initial COD (A), MLSS (B), cycle time (C), B2, C2, and BC were the significant model factors in SVI index. At optimal conditions, involving an initial COD of 1000 mg L−1, an organic loading rate (OLR) of 0.450 kg COD/m3d, MLSS of 3000 mg L−1, and cycle time of 24 h, we observed 94.6% of COD reduction, 98.5% turbidity removal, and 79 mL g−1 SVI. The results also showed that the kinetic of COD reduction and turbidity removal could be represented by the pseudo-second-order model.

To compare the performance and antibiotic-resistance character in different process configurations under different levels of antibiotics, anoxic/oxic-membrane bioreactors (MBR) 1#, MBR2# and a sequencing batch reactor (SBR) were operated with identical operating parameters. MBR1# and SBR were operated under high and increasing levels of antibiotics, MBR2# received constant and low concentration of antibiotics. Microbiological community and antibiotic resistance genes (ARGs) were investigated using 16S rDNA gene high-throughput sequencing and qPCR. More than 90% of penicillin and chlortetracycline were removed due to strong hydrolysis, followed by sulfamethoxazole (69.27%-86.25%) through biodegradation and norfloxacin (28.66%-53.86%) through adsorption. Process configuration affected total nitrogen removal more, while antibiotics concentration affected total phosphorus removal more. MBR1# outperformed SBR in reducing sulfamethoxazole, norfloxacin and ARGs due to the retention effect of the membrane module. Retention efficiency of ARGs in MBRs increased along the operation. Compared to the operational taxonomic unit (OTU) number before antibiotics addition, the OTU number in MBR1# and SBR decreased by 23.7% and 28.7%, while that in MBR2# kept relatively stable. Process configuration contributed to higher dissimilarity of microbial community than antibiotics concentration. The research provides an insight into the influence factors of antibiotics-containing wastewater treatment.

Polycyclic aromatic hydrocarbons (PAHs) and nitrated polycyclic aromatic hydrocarbons (NPAHs) are pollutants commonly present in the environment. Some NPAHs are considered to have more severe toxic effects than their parent PAHs. The existence of 16 PAHs (678.5–3817.8 ng/L in wastewater, 499.9 ng/g-1239.6 ng/g in sludge) and 5 NPAHs (175.8–1392.4 ng/L in wastewater, 483.5 ng/g-2763.1 ng/g in sludge) was determined in a biological wastewater treatment plant (WWTP) in Qingdao, China. Anthracene and naphthalene were the predominant PAHs, and 2-nitrofluorene and 9-nitroanthracene were the predominant NPAHs. Petroleum, liquid fossil fuel combustion and exhaust emissions were the main sources of PAHs and NPAHs in this study. In both the sequencing batch reactor/moving-bed biofilm (SBR/MBBR) and the anaerobic-anoxic-aerobic (A2O) process, low-molecular-weight PAHs were mainly removed through volatilization and biodegradation/biotransformation. Meanwhile, the removal of high-molecular-weight PAHs and NPAHs depended on adsorption and sedimentation. The transformation from PAHs to NPAHs mainly occurred in the aqueous-phase, especially in summer and that was confirmed by mass flow and ratios variation. Overall, the removal capacity of the A2O process for PAHs and NPAHs was better than that of the SBR/MBBR process. Tertiary treatment processes had little effect or even a negative effect on the removal of PAHs and NPAHs.

Due to the impact of methane, carbon dioxide and nitrous oxide on global warming, the quantity of these greenhouse gases (GHG) emissions from municipal wastewater treatment plants (WWTPs) has attracted more and more attention. Consequently, GHG emissions from the two popular treatment technologies: anaerobic/anoxic/oxic (AAO) process and sequencing batch reactor (SBR) should be properly identified and discussed toward the current situation in developing countries. Direct and indirect carbon dioxide (with and/or without including in Intergovernmental Panel on Climate Change (IPCC) report) are all discussed in this article. This literature study observed that a quantity of total carbon dioxide emissions from SBR (374 g/m3 of wastewater) was double that of AAO whilst 10% of these was direct carbon dioxide. Methane emitted from an SBR was 0.50 g/m3 wastewater while 0.18 g CH4/m3 wastewater was released from an AAO. The level of nitrous oxide from AAO and SBR accounted for 0.97 g/m3 wastewater and 4.20 g/m3 wastewater, respectively. Although these results were collected from different WWTPs and where influent was in various states, GHGs emitted from both biological units and other treatment units in various processes are significant. The results also revealed that aerated zone is the major contributing factor in a wastewater treatment plant to the large amount of GHG emissions.

Recent findings show that a subset of bacteria affiliated withNitrospira, a genus known for its importance in nitrite oxidation for biological nutrient removal applications, are capable ofcompleteammoniaoxidation (comammox) to nitrate. Early reports suggested that they were absent or present in low abundance in most activated sludge processes, and thus likely functionally irrelevant. Here we show the accumulation of comammoxNitrospirain a nitrifying sequencing batch reactor operated at low dissolved oxygen (DO) concentrations. Actual mainstream wastewater was used as influent after primary settling and an upstream pre-treatment process for carbon and phosphorus removal. The ammonia removal rate was stable and exceeded that of the treatment plant’s parallel full-scale high DO nitrifying activated sludge reactor. 16S rRNA sequencing showed a steady accumulation ofNitrospirato 53% total abundance and a decline in conventional ammonia oxidizing bacteria to Nitrospirabeginning around day 200, to eventually comprise 94% of all detectedamoAand 4% of total bacteria by day 407. Quantitative fluorescence in-situ hybridization confirmed the increasing trend and high relative abundance ofNitrospira. These results demonstrate that comammox can be metabolically relevant to nitrogen transformation in wastewater treatment, and can even dominate the ammonia oxidizing community. Our results suggest that comammox may be an important functional group in energy efficient nitrification systems designed to operate at low DO levels.

Aerobic granulation was successfully achieved in a pilot scale sequencing batch reactor within 40 days. Then, stability of different particle size granules was explored according to their activity and resistance to ultrasonic crushing. Different particle size granules (0.3–0.6 mm, 0.6–1 mm, 1–1.43 mm, 1.43–2 mm, 2–3 mm and 3–4 mm) were exposed under different ultrasonic power separately. It was found that the granules with 2–3 mm always had the maximum granulation rates after ultrasonic crushing. Meanwhile, activity data showed that the 2–3 mm granules had the lowest specific oxygen utilization rates, which indicated that they were easier to maintain stability as the increase of their particle sizes was the slowest. So, 500 mL mixed liquid of the reactor were taken out and sieved to obtain the 2–3 mm granules, which were subsequently returned to the reactor to increase their proportion. Through the manual regulation, the proportion of 2–3 mm granules kept increasing which gradually became dominant in the reactor. Under the strategy of 86 days of operation, the aerobic granules were regular and compact, which had good removal effects of the real wastewater. The results indicated that the stability of the system could be greatly enhanced by the method, which provided a new strategy to maintain the granular stability.

Because of its energy efficiency, the anaerobic ammonium oxidation (anammox) process has been recognized as the most promising biological nitrogen removal process, but its implementation in mainstream wastewater treatment plants is limited by its relatively high optimal temperature (30 °C). Recently, it was shown that during short-term batch experiments, reduced graphene oxide (RGO) displayed accelerated reaction activity at low temperatures (10–15 °C). In this study, the long-term effects of RGO on the low-temperature anammox process in a sequencing batch reactor (SBR), are studied for the first time, including different methods of interaction. The results presented here show that RGO can stimulate anammox activity up to 17% through two factors: bacterial growth stimulation, which was especially significant at higher temperatures (>15 °C), and an increase of the anammox reaction rate, which occurred only below 15 °C. The bacterial community structure was not influenced by addition of RGO. Moreover, after incubation in an anammox bioreactor, RGO showed signs of degradation and chemical changes as evidenced by the presence of oxygen and calcium on its surface. According to the literature and the obtained results, it is proposed that RGO is oxidized and oxygen is reduced by the organic mediator that is involved in the enzymatic reactions. However, activated sludge is a very complex structure created by numerous, undefined microorganisms, which makes it difficult to determine the exact oxidation mechanism.

We determined the effects of ex situ biological wastewater treatment on landfill stabilization under continuous circulation of leachate. Specifically, the waste composition and nitrogen in the leachate during leachate circulation (LC) alone was compared with that in a nitrified leachate circulation (NLC) system. An ex situ sequencing batch reactor (SBR) was applied in the NLC system to oxidize the ammonium to nitrite or nitrate, which was then circulated to landfill for denitrification to nitrogen gas. The chemical oxygen demand (COD) concentration in the leachate was low by NLC versus LC, because in the NLC system, ammonium was oxidized to nitrite/nitrate in the ex situ SBR, and aerobic decomposition and denitrification occurred simultaneously in the landfill, suggesting that the NLC system significantly improves the waste decomposition rate and accelerates landfill stabilization. Because denitrification in the landfill was activated in the NLC system and nitrite/nitrate was reduced to nitrogen gas, the proportion of nitrogen in the gas was higher compared with LC. LC, combined with an SBR, might have value in removing the nitrogen that is discharged from the leachate and in accelerating landfill stabilization, because landfill waste was used as the carbon source for denitrification.

In this study, a mesophilic two-phase anaerobic digestion system was used to treat waste activated sludge at the temperature of 35 ± 1 °C. The internal structure of the anaerobic sequencing batch reactor (methanogenic phase) has been improved by providing a solid–liquid separation plate, and a continuous-flow stirred tank reactor was employed as the acidogenic phase. The results of the study indicate that solid–liquid separation can be achieved in the methanogenic phase, and the low-temperature hydrolysis pretreatment can enhance solid–liquid separation capability. The separation of solids retention time and hydraulic retention time was also achieved in methanogenic phase, and the solids retention time was extended, which effectively improved the anaerobic digestion performance of the system. The organic concentration and total solids concentration in the methanogenic reactor were significantly different in height. The bottom of the reactor formed an area of high solids and low organic precipitation, while the upper part of the reactor formed a clear water area. The suspended solids concentration in the reactor clear water area was maintained at 359 ± 84 to 533 ± 93 mg/L, and the better solid–liquid separation effect was obtained inside the methanogenic phase. The maximum biogas yield was 258 ± 3 mL/g with the maximum volatile solids degradation rates of 59.43% in the system in Stage 3. Considering the efficiency of anaerobic digestion and the operating costs, the operating condition of Stage 4 (the designed hydraulic retention time was 10.67 d, the feed sludge was thermally pretreated, and its volume was 3 L) in this test is the optimal.