Stringent Discharge Standards Research Articles

Landscape of genes in hospital wastewater breaking through the defense line of last-resort antibiotics

Hospital wastewater contains abundant antibiotics, antibiotic resistance genes (ARGs), and pathogens. Last-resort antibiotic resistance genes (LARGs) include the New Delhi metallo-β-lactamase gene blaNDM, mobile colistin resistance gene mcr and tigecycline resistance gene tet(X) which confers resistance to carbapenems, colistin and tigecycline. The presence and significance of LARGs in hospital wastewater treatment systems (HWTS) have not yet been systematically explored. Here, LARG variants were shown to be prevalent both influents and effluents of HWTS. A total of 989 Enterobacteriaceae isolates that confer resistance to last-resort antibiotics were collected from effluents and multiple genetic contexts of LARGs were analyzed. LARGs-carrying plasmids were confirmed to show high multidrug phenotypes and transferability. We also discovered the co-occurrence of plasmids harboring blaNDM-1 and mcr-1 in single Escherichia coli, as well as E. coli HM016 containing two unique mcr-1-carrying plasmids. This result might accelerate co-dissemination of LARGs under environmental selection pressure. Different core genetic arrangements in these strains suggest several evolutionary pathways in HWTS. The resistance functions of LARGs were confirmed in vitro and in vivo by mass spectrometry. This study provides novel insights into the diversity, genetic context and function of critical ARGs in HWTS. The results raise the concern that LARGs may further spread into the environment, thus, more stringent discharge standards and regulations for hospital wastewater are urgently needed.

Multi-omic studies on the toxicity variations in effluents from different units of reclaimed water treatment

The conventional reclaimed water technologies could not effectively remove the micropollutants. Although the health risks of these residual micropollutants have been evaluated by model calculation, few animal-based studies have been performed, which is essential for risk verification. Here, we used transcriptomic, metabolomic, and other biochemical techniques to reveal the toxicity variations of effluents from oxidation ditch (OD), coagulation tank (CT), biological aerated filter (BAF), and ultraviolet disinfection pool (UV) in a reclaimed water plant located in Nanjing, China. No evident toxicity reduction trend was observed along the treatment units. Compared with control and other three treatment unit effluents, long-term exposure to reclaimed water (UV effluent) aggravated oxidative stress in mice and induced abnormal lipid metabolism and immune response. Moreover, striking correlations were identified between multi-omic biomarkers (4 differentially expressed genes and 8 significant changes metabolites) and residual micropollutants (40 semi-volatile organic compounds and 6N-nitrosamines). Our results strongly highlight that the health risks of reclaimed water are mainly induced by the residual micropollutants, and more advanced treatments and stringent discharge standards are needed to ensure the safety of reclaimed water.

Model construction and application for effluent prediction in wastewater treatment plant: Data processing method optimization and process parameters integration

Wastewater treatment based on the activated sludge process is complex process, which is easily affected by influent quality, aeration time and other factors, leading to unstable effluent. Facing increasingly stringent sewage discharge standards in China, it is necessary to build a prediction model for early warning of effluent quality. In this study, nine machine learning algorithms were adopted to construct models for the prediction of effluent Chemical Oxygen Demand (COD). In order to improve the prediction accuracy of the models, model optimization was conducted by introducing the hysteresis condition [Hydraulic Retention Time (HRT) of 18 h], data processing method (K-FOLD) and process parameters [dissolved oxygen (DO), sludge return ratio (SRR) and mixed liquid suspended solids (MLSS)]. Results showed that both K-Nearest Neighbour (KNN) and Gradient Boosting Decision Tree (GBDT) displayed excellent prediction effects, the best results of MAPE, RMSE and R2 were 7.34%/1.29/0.92(COD, KNN). The optimized models were further applied to the prediction of effluent total phosphorus (TP), total nitrogen (TN) and pH. The MAPE/RMSE/R2 were 7.43%/0.92/0.93(TN, GBDT), 17.81%/0.19/0.99(TP, KNN), 0.53%/0.16/0.99 (pH, KNN) respectively, indicating high prediction accuracy. The change and comparison of modeling conditions provide a new insight to wastewater prediction models. In addition, this study is close to the actual application scenario of WWTPs operation and management, also laying a foundation for the reverse regulation of energy saving and consumption reduction of wastewater treatment plants (WWTPs).

Development of aerobic granulation system for simultaneous removal of C, N, and P in sequencing batch airlift reactor

Conventional biological nutrient removal techniques often have disadvantages like low removal efficiencies, requirement of large footprint, and excess sludge production. Ever increasing stringent discharge standards demand for alternative technologies. In this context aerobic granular sludge (AGS) has evolved as a promising technology for complete nutrient removal. However, degradation of structural integrity of aerobic granules in long run is a prime concern of this technology. This work attempts to develop stable aerobic granules in an automated sequential batch airlift reactor (SBAR) for simultaneous C, N, and P removals under alternating aerobic and anoxic conditions. The reactor was operated at high sludge retention time (SRT). Combined operating strategies of varying dissolved oxygen (DO) concentration and feed cycle times were followed to optimize the conditions for effective granulation and subsequent removal efficiencies. Profiles of extracellular polymeric substances (EPS) and sludge volume index (SVI) were monitored. Optimum removal efficiencies of NH4+-N (92.7%), TN (90.6%), COD (90.1%), and PO43--P (83.2%), and granules of size 1.3–8 mm were achieved in phase IV at operational DO of 1–2 mg/L, and feeding intervals of 15 h and 9 h. NH4+-N (R2 = 0.97, k = 0.5093/h) and PO43--P (R2 = 0.95, k = 0.2574/h) removals were fitted well with first order kinetic model and that of COD (R2 = 0.97, k = 0.0032 L/mg/h) followed second order kinetics. This process is economical as effective biological nutrient and organics removal occurs in a single reactor without requirement of alkalinity supply, and negligible excess sludge production. The process requires small foot print and applicable for decentralized wastewater management in University campuses/tourist resorts/apartment complexes.

Coupling anammox with heterotrophic denitrification for enhanced nitrogen removal: A review

Anammox has been recognized as the current most cost-effective nitrogen removal process. However, the issue of excess nitrate residue from its effluent remains to be addressed in order to meet the increasingly stringent discharge standard. Other than nitrogen, certain types of wastewater have organic matter that also needs to be removed. Within this context, denitrification can be introduced to reduce nitrate produced in anammox process and improve effluent quality. Meanwhile, the organic content of wastewater can be also controlled. In such integrated system, maintaining the predominant role of anammox is of supreme importance in achieving the stable operation. This study reviews the strategies to establish a competition balance between anammox and denitrification processes by analyzing the kinetics of anammox and denitrifying microorganisms, discussing the favorable conditions in establishing the coupled process, and evaluating the system recovery approaches. Moreover, the dynamics of the microbial communities in response to the organic matters are also presented in order to better understand the complex interactions inside the system and provide a molecular insight in regulating the growth of the two functional bacteria for the stable coexistence. This review offers a guide for future engineering application on anammox coupled denitrification technology for advanced nitrogen removal.

Model-Based Solution for Upgrading Nitrogen Removal for a Full-Scale Municipal Wastewater Treatment Plant with CASS Process

Aiming at providing cost-effective approach for upgrading the existing municipal wastewater treatment plants in the cold region of China to meet more stringent discharge standards of nitrogen removal, a full-scale sewage treatment plant with the CASS process was selected through focusing on biological process, key equipment and hydrodynamics in bioreactors by the activated sludge model 1 (ASM1) and computational fluid dynamics (CFD) model. Influent COD fractions and the key characteristic parameters (YH and bH) of the activated sludge were determined through the respirometry at temperatures of 10 °C and 20 °C, respectively. The layout of submerged agitator installation in the bioreactor of the CASS process was optimized through CFD simulation. The calculation of the average relative deviation (less than 20%) between simulated data and the operation data, demonstrated that the ASM1 model could be reasonably used in the wastewater treatment plant simulation. The upgrade solution based on modelling of ASM1 and CFD was successfully applied in practice, which not only made the effluent COD, NH4+-N and TN concentrations meet with the discharge standard of Grade I-A, but also reduced the energy consumption by 25% and 16.67% in summer and winter, respectively. After upgrading, microbial diversity increased in both summer and winter, with an especially significant increase of the relative abundance of denitrifying bacteria.

Recent Advances in the Rejection of Endocrine-Disrupting Compounds from Water Using Membrane and Membrane Bioreactor Technologies: A Review.

Water is a critical resource necessary for life to be sustained, and its availability should be secured, appropriated, and easily obtainable. The continual detection of endocrine-disrupting chemicals (EDCs) (ng/L or µg/L) in water and wastewater has attracted critical concerns among the regulatory authorities and general public, due to its associated public health, ecological risks, and a threat to global water quality. Presently, there is a lack of stringent discharge standards regulating the emerging multiclass contaminants to obviate its possible undesirable impacts. The conventional treatment processes have reportedly ineffectual in eliminating the persistent EDCs pollutants, necessitating the researchers to develop alternative treatment methods. Occurrences of the EDCs and the attributed effects on humans and the environment are adequately reviewed. It indicated that comprehensive information on the recent advances in the rejection of EDCs via a novel membrane and membrane bioreactor (MBR) treatment techniques are still lacking. This paper critically studies and reports on recent advances in the membrane and MBR treatment methods for removing EDCs, fouling challenges, and its mitigation strategies. The removal mechanisms and the operating factors influencing the EDCs remediation were also examined. Membranes and MBR approaches have proven successful and viable to eliminate various EDCs contaminants.

Analysis and Optimization of Shale Oil Refinery Wastewater Treatment Process

Shale oil refinery wastewater was a kind of industrial wastewater with many types of organic matter and complex water quality. It contains a large amount of pollutants such as phenols, ammonia and oil, which is extremely harmful to the environment. Due to the increasingly stringent national discharge standards, it was difficult to treat wastewater up to standard with only one method, and multiple methods are needed to jointly treat wastewater. In this paper, the process of shale oil refinery wastewater treatment system was modified, and the “SDN+Advanced Oxidation+MBR” process was proposed to treat wastewater.

Effect of electrode materials on the degradation of palm oil mill effluent by electro-oxidation process

In the recent decades, Malaysia has been known as the one of the palm oil producers and exporters. The increasing of the production and demand of palm oil tends to increase the Palm Oil Mill Effluent (POME). Undeniably, the conventional biological treatment has been implemented to reduce the organic matters but insufficient to satisfy the discharge standard by the local authority. Consequently, the biological treated POME has to be treated further to meet the stringent discharge standard. Hence, an advanced oxidation processes (AOPs), electro-oxidation process (EOP) has been applied to treat further the biologically treated POME. There are two stages in this study, EOP carried on with catalyst and electrode (Al and Fe). Therefore, the performance of EOP is evaluated by investigating the removal efficiency on the organic parameters like COD, colour, suspended solid and NH3-N. The operational parameters are the pH adjustment (pH 3, 5, 7 and 9), contact time ranging from 0 to 60 min and the dosage of catalyst (H2O2 and TiO2). The highest degradation of the parameters was obtained under the most acidic solution pH 3, with addition of TiO2 by using Al electrode. The percentages of removal are 96.58 % of colour, 98.74 % of SS and 84.85 % of COD.

Selection of chemical phosphorus removal scheme based on Analytic Hierarchy Process

Chemical precipitation phosphorus removal process can improve the phosphorus removal effect of sewage treatment system to meet the increasingly stringent discharge standards. In order to assist designers in selecting reasonable chemical phosphorus removal schemes, the analytic hierarchy process was applied to quantitatively evaluate each chemical phosphorus removal scheme from four aspects: water treatment effect, operation cost, operation and management difficulty and environmental impact. Finally, combined with an engineering example, the process of analytic hierarchy process quantitative evaluation of chemical phosphorus removal scheme and the method of selecting the optimal scheme are introduced, which provides a reference for the selection of chemical phosphorus removal scheme in engineering.

Differences of bacterial communities in two full-scale A2/O municipal wastewater treatment plants and their effects on effluent total nitrogen removal

Bacterial communities and functional bacteria played a vital role in the biological removal of nitrogen in wastewater. Bacterial communities, nitrogen removal and their correlationship were compared and analyzed in two full-scale anaerobic/anoxic/aerobic (A2/O) municipal wastewater treatment plants (WWTPs) (assigned as D and X plants). Illumina high-throughput sequencing results showed remarkable differences in the bacterial communities’ diversity were found between these two WWTPs. Significant differences in species diversity existed in anaerobic, anoxic, and aerobic tanks in X plant, while no significant differences were found among the D plant’s tanks. In the aerobic tanks of X and D plants, nitrifying bacteria genera accounted for 5.29% and 1.57%, respectively, while aerobic denitrifying bacteria accounted for 0.64% and 0.47%. In the two plants’ anoxic tanks, denitrifying bacteria accounted for 1.14% and 1.64%, respectively. During the two months of monitoring, average effluent total nitrogen (TN) concentrations of X and D plants were 14.85 ± 1.85 and 17.66 ± 0.92 mg/L, respectively, and the former was satisfied with the stringent discharge standard. Effluent TN was significantly negatively correlated with Nitrospira, Denitrobacter, Thauera, Comamonas and Dechloromonas (P<0.05) and positively correlated with Paracoccus and Dokdonella (P<0.05). Overall, species diversity in each functional tank of X plant was remarkably different, and functional genera were more abundant in X plant than that in the D plant, which might be one reason for the lower effluent TN concentrations in the two WWTPs.

Phytoremediation of Vegetable Leachate by Nymphaea Nouchali

Leachate normally contains high concentration of pollutants and regulated under stringent discharge standards. Conventional treatments of leachate are no longer adequate to ensure compliance with the standard. Phytoremediation is a relatively new approach to treat leachate contaminated by organic and inorganic substances. Nymphaea Nouchali is an abundant and easy-growing free-floating aquatic plants found in the rice fields, reservoir and polluted ponds. Nymphaea and Nuphar are the most commonly found species in Malaysia. In the last few decades there has been an increasing interest in the study of phytoremediator plants which can serve as an alternative for leachate treatment. The main objective of this study is to determine the effectiveness of organic removal from vegetable leachate (VL) using Nymphaea Nouchali. The results exhibited that after 7 days of phytoremediation, sample R0.5 shows excellent removal of biological oxygen demand (BOD), chemical oxygen demand (COD), colour and suspended solid (SS) to meet the allowable limit.

Iron-enhanced primary sedimentation and acidogenic sludge fermentation to achieve self-sufficient organic carbon supply for enhanced nutrient removal in wastewater treatment✰

To treat municipal wastewater with a low carbon to nitrogen ratio, the addition of an external carbon source is often needed to achieve enhanced nutrient (nitrogen and phosphorus) removal. To meet this need, this research developed an innovative strategy for reserving and utilizing organic pollutants to achieve a self-sufficient organic carbon supply for wastewater treatment. In the new system, before biological treatment by a sequencing batch reactor (SBR), Fe-based chemically enhanced primary sedimentation (CEPS) was used to reserve part of the organics from the wastewater in the CEPS sludge. By acidogenic fermentation in the side-stream, the settled organics in the CEPS sludge were converted into volatile fatty acids and other soluble organics to provide a suitable carbon source for denitrification in the anoxic phase of the SBR. The experimental results showed that the new SBR system integrated with CEPS and acidogenic sludge fermentation removed up to 89% of the total phosphorus (TP) and 83% of the total nitrogen (TN) from the wastewater. Compared with the conventional SBR system, TP and TN removal was increased by more than 65% and 50%, respectively. As well as increasing nutrient removal efficiency without the need for external carbon addition, the Fe-based CEPS greatly reduced the organic load on the SBR biological treatment process, reducing the aeration cost. Overall, a cost-effective wastewater treatment process is developed that can be used to upgrade existing wastewater treatment plants to improve the nutrient removal performance and meet more stringent discharge standards.

Mainstream nitrogen separation and side-stream removal to reduce discharge and footprint of wastewater treatment plants

The activated sludge process is efficient for pollutant removal, but was criticized for its large upfront investment and land area requirements. Improving nitrogen removal to levels sufficient to reduce eutrophication is a challenge to conventional nitrification and denitrification, which is limited by process configuration (with nitrate recirculation) and environmental inhibition. To satisfy stringent discharge standards within a compact plant footprint, a sustainable strategy by moving nitrogen removal from mainstream to side-stream is designed by a cycle of ammonium exchange, regeneration and nitrogen removal (AERN), combined with biological and physiochemical technologies. Ammonium was rapidly captured by ion exchangers, then exchanged into regenerant, and converted to N2 by chlorination or Sharon-anaerobic ammonia oxidation in the side-stream. The AERN cycle can be combined with a high-rate anaerobic/aerobic process and chemical phosphorus removal to construct a HAERN process, or inserted between a coagulation-sedimentation tank and a membrane bioreactor to construct a CAERNM process. Two AERN-based systems both achieved efficient pollutants removal (especially for nitrogen removal of 86.8–93.7%) in long-term running, and didn't impair exchange capacity and properties of ion exchangers. Compared with the conventional anaerobic/anoxic/aerobic process, AERN-based processes reduce land occupancy, upfront investments, and treatment costs by 59.9–71.1%, 25.5–38.0% and 2.3–31.0%, respectively.

Electro-oxidation as Tertiary Treatment Techniques for Removal of Palm Oil Mill Effluent

The production of palm oil, though, results in the generation of huge quantities of polluted wastewater normally referred as palm oil mill effluent (POME). It gives adverse impacts to the environment, particularly if it is not properly treated. POME are known to have various types of liquids, residual oil and suspended solid as it has very high strength waste in its untreated form. Although conventional biological processes are normally efficient for the degradation of pollutants occurring in wastewater, most of these compounds are not effectively removed. As a result, further treatment is needed to meet more stringent discharge standards of Department of Environment (DOE), Malaysia. This research focused on treatment of POME by using electro-oxidation process (EO). It was done to identify the performance of EO process for colour, chemical oxygen demand (COD), suspended solids (SS), and Ammoniacal-nitrogen NH3-N) removal as well as the relative effects of different operational parameters such as pH, type of electrodes and contact time. The pH was varied between 3 and 11, using Ferum (Fe) and Aluminium (Al) electrode, and contact time from 0 to 120 min. The most suitable pH, contact time and type of electrode were pH 3, 120 min and Aluminium electrode, respectively. Therefore, EO process at specified level can be used as an efficient and effective post-treatment technology to meet the standard regulatory requirements.

A self-sustaining synergetic microalgal-bacterial granular sludge process towards energy-efficient and environmentally sustainable municipal wastewater treatment

Globally increasing concerns have been raised on the high energy consumption and greenhouse gas emissions in conventional municipal wastewater treatment processes over the past decades. In this study, a self-sustaining synergetic microalgal-bacterial granular sludge process was thus developed to address these challenges. The results showed that the microalgal-bacterial granular sludge process was capable of removing 92.69%, 96.84% and 87.16% of influent organics, ammonia and phosphorus under non-aeration conditions over a short time of 6 h. The effluent could meet the increasingly stringent discharge standards in many countries worldwide. A tight synergetic interrelationship effect between microalgae and bacteria in granules was essential for such excellent process performance. The stoichiometric and functional genes analyses further revealed that most of organic matter and nutrients were removed through microalgal and bacterial assimilations. Moreover, it was found that there existed a desirable distribution of functional species of microalgae and bacteria in microalgal-bacterial granules, which appeared to be essential for the self-sustaining synergetic reactions and stability of microalgal-bacterial granules. Consequently, this work may offer a promising engineering alternative with great potential to achieve energy-efficient and environmentally sustainable municipal wastewater treatment.

What’s the best way to achieve successful mainstream partial nitritation-anammox application?

Partial nitritation-anammox (PN-A) process, which significantly reduces energy and chemical input compared to the conventional biological nitrogen removal process, is a game-changing nitrogen-removal alternative. PN-A treating municipal wastewater (mainstream PN-A) may shed light on achieving a more sustainable energy-neutral municipal wastewater treatment, but practical applications are still not available. This review is therefore critically conducted to identify the challenges impeding the application of mainstream PN-A. At temperatures ≥ 25 °C, PN-A process treating mainstream wastewater can achieve comparable nitrogen removal performance to conventional processes, but the effluent quality may need to be improved to meet stringent discharge standards; at temperatures < 20 °C, long-term process instability, low nitrogen removal efficiency, and poor effluent quality are the main operating difficulties. The reasons are attributed to challenges in maintaining sufficient anammox activity and effective NOB suppression. A framework of operable solutions to these difficulties and challenges is suggested, among which the efficient anammox biomass retention should be prioritized. The effectiveness and practical availability of these solutions are also assessed. Ultimately, depending on technological readiness, a roadmap for the PN-A application is proposed to make the best of the benefits of PN-A and promote the implementation of energy-neutral/positive municipal wastewater treatment.

Removal of palm oil mill effluent by using electro-oxidation process

Wastewater includes the Palm Oil Mill Effluent (POME) that gives adverse impacts to the environment especially for water pollution when it is not treated properly. POME are known to have various types of liquids, residual oil and suspended solid as it has very high strength waste in its untreated form. Although conventional biological processes are normally efficient for the degradation of pollutants occurring in wastewater, most of these compounds are not effectively removed. As a result, further treatment is needed to meet more stringent discharge standards of Department of Environment (DOE). This research focused on treatment of POME by using electro-oxidation process (EO). It was done to identify the performance of EO process for colour, chemical oxygen demand (COD), suspended solids (SS), ammoniacal-nitrogen (NH3-N), and turbidity removal as well as the relative effects of different operational parameters such as pH, type of electrodes and contact time. The pH was varied from 3 to 11, the electrodes were aluminium and iron and the contact time was from 0 to 120 min. The most suitable pH, contact time and type of electrode were pH 3, 120 min and Al electrode.

Effects of deoxygenation pretreatment and dissolved oxygen adjustment on performance of double-layer-packed sequencing biofilm batch reactor treating secondary effluent under low temperature

To meet the increasing stringent discharge standards, many wastewater treatment plants (WWTPs) are impelled to execute tertiary treatment, among which advanced nitrogen removal is still the key. An effective alternative for advanced nitrogen removal is sequencing biofilm batch reactor (SBBR), whose performance is closely related to dissolved oxygen (DO). In this study, the effects of deoxygenation pretreatment during anoxic phase and DO adjustment during aerobic phase on performance of double-layer-packed SBBR treating a typical carbon-lacked (COD/TN = 2.0, dominated with ammonium) secondary effluent under low temperature (15 °C) were investigated. It was found that deoxygenation pretreatment via adding sulfite had no significant impact on organics/phosphorus removal or nitrification but significantly improved denitrification. The deoxygenation stimulated nitrite accumulation leading to a higher simultaneous nitrification and denitrification (SND) rate. Similarly, with the increase of DO during aerobic phase, nitrification capacity increased while denitrification intensity decreased. When DO ≥ 3.5 mg/L, total ammonium nitrogen (TAN) in final effluent met the first A standard (GB 18918-2002, China). When DO at 2.5 mg/L, a highest denitrification intensity was observed while neither TAN nor total nitrogen (TN) in final effluent met the discharge standards probably mainly due to low temperature and carbon shortage. Among all the tests, FA and FNA were not the main causes for nitrite accumulation. The above findings might be helpful in guiding practical applications.

Combined heterotrophic and autotrophic system for advanced denitrification of municipal secondary effluent in full-scale plant and bacterial community analysis

Total nitrogen (TN) removal is the major technical challenge for wastewater treatment plants to meet the more stringent discharge standard. In this study, lab- (0.05 m3/d), pilot- (1000 m3/d) and full-scale (10,000 m3/d) combined heterotrophic and autotrophic denitrification reactors (HARs) were designed and operated to treat municipal secondary effluent. During the 110-day stable operation, the effluent TN was reduced below 2.5 mg/L without secondary pollution causing by the excessive addition of organics, close to Class IV of Environmental Quality Standards for Surface Water. The bacterial richness and diversity increased with the expansion of reactor scale. Denitrifying bacteria (DB) dominated in all reactors, however, Thiomonas (12.42%), Methylotenera (6.35%), Thiobacillus (20.62%), Methyloverstatilis (5.44%) and Thauera (8.21%) were the main genera in lab-, pilot- and full-scale reactors respectively. The denitrification efficiency temporarily deteriorated at the later stage, and redundancy analysis (RDA) indicated the obviously increased sulfate reducing bacteria (SRB) and sulfide were main contributors. Sludge supplement rapidly recovered the reactors performance in five days. This study suggests that HARs could be a promising technique for advanced denitrification of the municipal secondary effluent.