Improvement Of Effluent Quality Research Articles

Novel membrane bioreactor with iron-tannin-framework based membrane for effluent quality improvement and fouling control

A 10 L membrane bioreactor (MBR) was constructed with novel iron-tannin-framework ultrafiltration membrane (ITUM) for membrane fouling mitigation and effluent quality improvement. Compared to commercial ultrafiltration membrane (CUM) in the same MBR, ITUM exhibited hydrophilicity with a contact angle of 64.18° (71.36° for CUM), resulting the permeance of ITUM (50.2 L m-2h−2 bar−1) 1.8 times higher than CUM. During 70-day operation, ITUM was consistently run at lower transmembrane pressure. After operation, the polyethersulfone (PES) peak intensity of ITUM reduced less than 1 % (85 % for CUM), which indicated a thinner sludge layer on ITUM. Meanwhile, the average effluent chemical oxygen demand concentration for ITUM and CUM achieved 16.69 and 17.60 mg L-1 in stable phase, respectively. For NH4+-N, it could reach 0 and 0.04 mg L-1. 16 s RNA results showed that Saccharibacteria accounted for 1.48 % and 1.20 % on ITUM and CUM, respectively. According to first-principles density functional theory simulations, simulated adsorption energies was −1.330 eV for gram-positive bacteria (such as Saccharibacteria). It was −0.867 eV for Fe(Ⅲ) to gram-negative bacteria. It suggests that ITUM could easily attract microorganisms with the ability of polysaccharide degradation, while reducing this type of pollutants deposition on membrane. Therefore, the ITUM received a more superior effluent quality and membrane fouling resistance.

Does stricter sewage treatment targets policy exacerbate the contradiction between effluent water quality improvement and carbon emissions mitigation? An evidence from China

Rapid expansion and upgrading of wastewater treatment facilities globally, driven by stricter wastewater policies, significantly contribute to carbon emissions. China has contributed 30 % of carbon emissions in the world, 1 % of which comes from wastewater treatment, necessitating more understanding of the impact of policies, especially the stringent “10-Point Water Plan” policy. From a micro perspective, this study uses the difference-in-differences method to analyze the impact of wastewater treatment policies on water and carbon issues in China’s 2894 wastewater treatment plants (WWTPs), and delves into the heterogeneity, and mechanisms across various dimensions. The results show that stricter sewage treatment policy decrease effluent concentration of the chemical oxygen demand (COD) by 2.35 %, and also cause a 1.74 % rise in carbon emissions per 10,000 m3 of wastewater treated, intensifying the short-term contradiction, while the contradictions may fall in the long term. It is more significant in southern regions and the cities with lower environmental regulation intensity. Also, there are significant differences in different wastewater treatment technology and scale. Significant improvements in effluent water quality are observed in WWTPs with 100,000 to 200,000 m3/day capacity and those using biofilm treatment technology. Through mechanism analysis, reasonable expansion of urban pipelines and WWTPs, promotion of biofilm treatment technology, reduction of energy consumption, and improvement of pollutant reduction efficiency are feasible paths to improve water quality and reduce carbon emissions. This research provides a perspective on solving water-carbon contradictions in WWTPs, holding critical significance for urban wastewater treatment and carbon emission management.

Effluent quality improvement in sequencing batch reactor-based wastewater treatment processes using advanced control strategies.

The treatment of wastewater is highly challenging due to large fluctuations in flowrates, pollutants, and variable influent water compositions. A sequencing batch reactor (SBR) and modified SBR cycle-step-feed process (SSBR) configuration are studied in this work to effectively treat municipal wastewater while simultaneously removing nitrogen and phosphorus. To control the amount of dissolved oxygen in an SBR, three axiomatic control strategies (proportional integral (PI), fractional proportional integral (FPI), and fuzzy logic controllers) are presented. Relevant control algorithms have been designed using plant data with the models of SBR and SSBR based on ASM2d framework. On comparison, FPI showed a significant reduction in nutrient levels and added an improvement in effluent quality. The overall effluent quality is improved by 0.86% in FPI in comparison with PI controller. The SSBR, which was improved by precisely optimizing nutrient supply and aeration, establishes a delicate equilibrium. This refined method reduces oxygen requirements while reliably sustaining important biological functions. Focusing solely on the FPI controller's performance in terms of total air volume consumption, the step-feed SBR mechanism achieves an excellent 11.04% reduction in consumption.

Investigation of the performance of the combined moving bed bioreactor-membrane bioreactor (MBBR-MBR) for textile wastewater treatment

The present study focused on the investigation of the performance of a Moving Bed Bioreactor coupled with a Membrane Bioreactor (MBBR-MBR) on a small scale for textile wastewater treatment. The parameters examined in this study included the removal efficiency of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), turbidity, color, and heavy metals (HM). The two reactors were operated consecutively and maintained aerobic conditions. The idea is to reduce the pollutant load significantly through the activity of microorganism attached to the biofilm covered carriers in MBBR and successive membrane filtration. The system demonstrated a favorable outcome even in a smaller hydraulic retention time (HRT) of 1 day, which presents a significant advantage in terms of cost and space saving. The removal effectiveness of COD attained a maximum of 92 %, BOD reached a maximum of 95 %, and the color removal performance obtained a removal efficiency of 87 %. Furthermore, the treatment showed remarkable efficiency in removing up to 100 % of TSS and 96 % of turbidity. Additionally, an evaluation was conducted on the elimination of heavy metals, including Zinc (Zn), Lead (Pb), Chromium (Cr), and Iron (Fe). The efficacy of removing these HMs was found to exceed 85 %. All these favorable outcomes contribute to the improvement of effluent quality, mitigation of contamination hazards, and fouling reduction.

Removal of Anabaena by ultrasonic pretreatment enhancing-coagulation and water treatment processes

Cyanobacteria bloom brings great challenges to the safety of the drinking water process. Ultrasonic pretreatment can effectively enhance coagulation to remove algae cells from algae-laden water. However, due to the special chain-like structure of Anabaena, the removal characteristics of Anabaena in water treatment process are quite different from those of unicellular cyanobacteria. No study has yet systematic studied on the enhancement effect of ultrasonic enhanced water treatment process on Anabaena. Therefore, this paper studied the characteristics and mechanism of ultrasonic pretreatment to enhance the removal of Anabaena, and carried out pilot experiments. The results showed that ultrasound irradiation at 740 kHz and 1.12 MHz had a great effect on the destruction of the chain-like structure and cell structure of Anabaena. After 15 min, the removal rate of Anabaena cells reached 16.0% and 30.4%, respectively, and the release of intracellular organic matter (IOM) reached 4.3 and 6.0 mg/L, in which phycocyanin released more. The damage of dynamic ultrasound irradiation on algae cells is weak, which can avoid the influence of uneven ultrasound irradiation on algae cells. The enhanced coagulation effect was better after 740 kHz ultrasonic pretreatment for 1 min, and the removal rates of algal cells, turbidity and dissolved organic carbon (DOC) increased by 7%, 9.4% and 12.6%, respectively. Pilot scale experiments demonstrate that ultrasonic pretreatment leads to a notable enhancement in the removal efficiency during the coagulation and sedimentation stages. After 4 h of operation, the turbidity and algal cell removal in the sedimentation stage increased by 6.1% and 14.0%, respectively. In addition, the removal of DOC in the final treated water increased by 6.7%. Furthermore, the disinfection by-products (DBPs) concentration experiences a reduction exceeding 200 μg per liter. Together, these results show a substantial improvement in filtration efficiency and effluent quality. This study provides guidance for the ongoing study of ultrasonic pretreatment to remove chain-like cyanobacteria.

Nitrogen and phosphorus removal performance of sequential batch operation for algal cultivation through suspended-solid phase photobioreactor

Nitrogen (N) and phosphorus (P) absorbed by algae in the suspended-solid phase photobioreactor (ssPBR) have emerged as an efficient pathway to purify the effluent of wastewater treatment plants (WWTPs). However, the key operational parameters of the ssPBR need to be optimized. In this study, the stability of the system after sequential batch operations and the efficiency under various influent P concentrations were evaluated. The results demonstrated that the ssPBR maintained a high N/P removal efficiency of 96 % and 98 %, respectively, after 5 cycles. When N was kept at 15 mg/L and P ranged from 1.5 to 3.0 mg/L, the system yielded plenty of algae products and guaranteed the effluent quality that met the discharge standards. Notably, the carriers were a key contributor to the high metabolism of algae and high performance. This work provided theoretical ideas and technical guidance for effluent quality improvement in WWTPs.

Novel insight into secondary effluent quality improvement and ultrafiltration fouling mitigation by UV/peracetic acid pretreatment

Ultrafiltration (UF) technology is widely used in the treatment for deep purification of municipal secondary effluent, however, the membrane fouling and low removal of N, P, and organic matter during actual operation have been the main bottlenecks limiting its wide-spread application. To address the above problems, this study employed peracetic acid (PAA) and UV/PAA to evaluate the effects of PAA-based pre-oxidation on ultrafiltration membrane fouling and secondary effluent water quality. The results demonstrated that the activated PAA pre-oxidation could prominently enhance the hydrophilicity of effluent organic matter, effectively destroy the high molecular weight organic matter and mineralize the low molecular weight organic matter. PAA and its metabolites, as well as the by-products of EfOM, increased the C/P ratio in water samples from 118 to 563 and the C/N ratio from 0.86 to 8.53. After UV/20 mg/L PAA pretreatment, the reversible and irreversible membrane fouling resistance significantly decreased by 55.97 % and 65.67 %, respectively. Moreover, the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory showed lower adhere potential of the foulants to the membrane surface. In general, UV/PAA as ultrafiltration pretreatment has a huge potential for secondary effluent treatment for membrane fouling mitigation and water quality improvement.

An overlooked crystallization effect during the O3 participated coagulation improves the performance of dual-membrane process

Till now, the transformation of amorphous flocs formed during the hydrolysis stage of coagulation has not been fully addressed. In this work, by using a conventional coagulant (alum), the transformation process was explored by observing the interactions between O3 and the amorphous alum flocs formed during flocculation at neutral pH. It was found that O3 promoted the transition of the in-situ formed alum flocs from tetrahedral Al (Al(O)4) to octahedral Al (Al(O)6) structures, through an accelerated dehydroxylation process, and therefore facilitated the crystallization process to form boehmite. During this process, the surface functional groups of amorphous Al flocs (Al–H2O and Al–OH) were observed to take part in the O3 catalytic oxidation with the generation of hydroxyl radicals (OH). This synergistic effect significantly favored the performance of the subsequent dual-membrane (UF-NF) process in terms of both fouling alleviation (1.78 and 1.60 times higher flux of UF and NF, respectively) and final effluent quality improvement, including the reduction in disinfection byproduct (DBP) formation potential (48.1% and 22.4% lower generation of total trihalomethanes and total haloacetic acid, respectively) and the corresponding calculated toxicity. The results obtained here provide a greater understanding of the transformation of amorphous Al flocs formed during flocculation with O3, and valuable information regarding its practical application in membrane filtration process with greater treatment performance.

Nitrous oxide reduction in wastewater treatment plants by the regulation of the internal recirculation flow rate with a fuzzy controller

The reduction of greenhouse gas emissions due to anthropogenic causes is one of the world's main challenges to face climate change. Wastewater treatment plants are necessary to improve the quality of wastewater before it is discharged into the receiving environment, but they have the disadvantage of generating nitrous oxide emissions during the biological treatment, which is a potent greenhouse gas. Avoiding partial nitrification by increasing dissolved oxygen is one of the ways to reduce these emissions. However, this article proposes to face a reduction of nitrous oxide emissions by reducing oxygen to minimum levels causing heterotrophic microorganisms to reduce nitrous oxide to dinitrogen. To achieve this objective, the present work proposes a regulation of the internal recirculation flow rate of the biological treatment by means of a fuzzy controller. This regulation is added to a usual control strategy in wastewater treatment plants, which achieves satisfactory results with respect to water quality and operational costs but that generates high nitrous oxide emissions. The Benchmark Simulation Model no. 2 Gas is used as working scenario, which includes the two main nitrous oxide emission pathways: heterotrophic denitrification and ammonia oxidizing bacteria denitrification. The proposed internal recirculation manipulation is shown to achieve nitrous oxide reductions of 26.70 and 30.83 % in different time periods with a slight effluent quality improvement and an operational cost reduction.

Electro-enhanced rapid separation of nanosized oil droplets from emulsions via the superhydrophilic micro-sized pore membrane

Waste oil-in-water emulsion is a special and unmanageable oily wastewater produced by several industries. Based on the sieving effect, the use of a membrane is a promising method to separate emulsion, whereas low flux remains a fundamental challenge. In this study, the coupling of an electric field with superhydrophilic fibrous membranes helped separate micro-/nano- paraffin in water emulsions (247–1887 nm) stabilized by SDS (100–500 mg/L) with a general applicability. The micro-sized pore membrane (0.634 μm) achieved outstanding rejection of nano-sized oil droplets (247 nm) using an electric field. It promoted flux from 1,202 to 18,388 LMH/bar by 1,429 % which was more than that in other literature by 1–2 orders of magnitude and improved oil removal from 97.61 % to 99.88 %. The reduction of equivalent pore size of membrane by the double layer force and the promotion of coalescence of oil droplets driven by the Laplace force rooted in the fibrous spindle of the membrane achieved enhanced selectivity. Electrophoretic force and double layer force mitigated the formation of the filter cake and irreversible fouling, respectively, to promote permeability and antifouling. This research provides a method for the simultaneous promotion of flux and improvement in effluent quality using an electric field, which breaks the limit of the trade-off effect.

Hybrid powdered activated carbon-activated sludge biofilm formation to mitigate biofouling in dynamic membrane bioreactor for wastewater treatment

Membrane costs and biofouling limit applications of membrane bioreactors (MBRs) for wastewater treatment. Here, powdered activated carbon (PAC) utilization in the formation and performance of a self-forming dynamic membrane consisting of activated sludge and PAC during hybrid wastewater treatment process was studied. Short-term agitation helped (non)biological particles to quickly uniformly settle on mesh filter, forming more uniform PAC-containing dynamic membranes (PAC-DMs). PAC adsorbed adhesive materials, resulting in an increase in average floc size and DM permeability while decreasing biofouling. The most efficient PAC concentration was 4 g L−1 considering techno-economics, i.e. the highest effluent quality (turbidity of 19.89 NTU) and the lowest biofouling (transmembrane pressure rise of 2.89 mbar). Short-term performance of hybrid PAC-DM bioreactor (PAC-DMBR) showed stability in effluent quality improvement including 92%, 95%, 83%, 84% and 98% reductions in turbidity, chemical oxygen demand, total dissolved solids, total nitrogen, and total phosphorous, respectively. Accordingly, adopting hybrid PAC-DMBR has potential to alleviate biofouling and capital cost.

Solar photo-Fenton mediated by alternative oxidants for MWWTP effluent quality improvement: Impact on microbial community, priority pathogens and removal of antibiotic-resistant genes

Municipal wastewater treatment plant effluent (MWWTPE) contains thousands of resistant strains which carry numerous genes and their variants. Avoiding the spread of these contaminants to the environment is a public health concern. Although solar photo-Fenton has been proved an effective complementary method for the control of antimicrobial resistance in MWWTPE, the use of persulfate (PS) as an oxidant for the elimination of antimicrobial-resistant bacteria and genes in the photo-Fenton treatment is still underexplored. This study aimed to investigate PS-mediated solar photo-Fenton (solar/Fe2+/S2O82−), and a combined oxidant system (solar/Fe2+/H2O2 + S2O82−) for the removal of ARB and ARGs from MWWTPE. Solar/Fe2+/S2O82− reached the lowest richness and diversity of microbial community, along with effective removal of the main phyla originally present in MWWTPE (88% of Proteobacteria, 99% of Bacteroidetes, and complete removal of Chlroflexi), 44% removal of total ARGs, and 99% removal of M. tuberculosis. Yet, it led to a 35-fold enrichment for Firmicutes. Hence, it is critical to investigate tolerance mechanisms pertaining to this group. In contrast, the combined oxidant system did not significantly impact alpha diversity of microbial community originally present in MWWTPE (p-value > 0.1), so being less efficient for ARB elimination than the solar/Fe2+/S2O82−. This was not expected as co-occurring reactions in this system should lead to a higher number of reactive radicals (SO4•− and HO•). Furthermore, it also caused positive selection of Firmicutes (>8-fold) and Proteobacteria (>2-fold). Nonetheless, the combined oxidant system resulted in total DNA fragmentation. Thus, it is important to promote further investigation of mechanisms involved in bacteria inactivation and DNA damage in the combined oxidant system.

Technical Note 8 - Applicability of support medium based of polyurethane foam for systems used to post-treatment of anaerobic effluents

Several technologies have been applied to post-treat anaerobic effluents. For most of those, a rigorous sludge management is needed. In this case, the use of sponge-based packing media in biofilm systems tends to significantly contribute to the minimization of sludge production and effluent quality improvement. Endogenous respiration and predation are important mechanistic processes explaining such improvements, which is related with the increase of the sludge retention time by the retention of biomass within the sponge. Depending on the operational condition, nitrogen removal is also observed in addition to the notorious performance for organic matter removal. Considering the advances for the post-treatment of anaerobic effluents with the use of sponge-based biofilm systems, this Technical Note aim to present: (i) fundamentals of biofilm systems using polyurethane sponge as support media; (ii) full-scale experiences with emerging sponge-based technologies; (iii) performance of sponge-based biofilm systems and operational conditions usually practiced; (iv) a preliminary critical analysis regarding implementation and operational costs; (v) advantages and disadvantages. The potential and limitations regarding the use of sponge-based reactors as post-treatment of anaerobic effluents are finally remarked.

Solar Photo-Fenton Mediated by Alternative Oxidants for Mwwtp Effluent Quality Improvement: Impact on Microbial Community, Priority Pathogens and Removal of Antibiotic-Resistant Genes

Solar Photo-Fenton Mediated by Alternative Oxidants for Mwwtp Effluent Quality Improvement: Impact on Microbial Community, Priority Pathogens and Removal of Antibiotic-Resistant Genes

Identifying active concentrations of biopolymers for enhancing membrane nanofiltration performance: From bench-scale tests to real production considerations

In the last decades, membrane-based nanofiltration (NF) technique has been widely applied for safe and high-quality drinking water production worldwide. NF membrane fouling has become one of the main obstacles in its application due to high operation cost, and thus numerous efforts have been made. However, there is still a large disconnect between academic findings and their applications. Hence, novel approaches for further exploitation and application are required based on feasibility of implementation. In this work, an optimized design of membrane-based NF plants was proposed, inspired by natural biopolymers present in feed water of NF unit. Specifically, we found beneficial functions of biopolymers, including NF membrane fouling alleviation and effluent quality improvement; these advantages could only be “activated” under a certain concentration range of biopolymers (0–1 mg C/L here), and less or more is not acceptable. This indicated that a NF unit is better to follow a microfiltration (MF) (instead of ultrafiltration (UF) which removes biopolymers) process during which natural biopolymers could be remained; also, this approach is suggested to be valid across different seasons when biopolymers' concentrations could be controlled within an “activated” range by mixing MF and UF permeates. Furthermore, three representative reference biopolymers with different, confirmed spatial structures and molecular weight (MW) were used to elucidate the micro-level functions of natural biopolymers on NF membranes, suggesting that cake layer structures shaped by various biopolymers determine the resulting NF performance. Overall, this innovative proposal is expected to be considered and adopted towards more energy-efficient NF technology for drinking water supply.

Effects of biochar on the growth of Vallisneria natans in surface flow constructed wetland.

To improve the nitrogen and phosphorus removal efficiency of surface flow constructed wetlands (SFCWs), biochar was added to an SFCW matrix. The effects of adding different amounts of biochar on water purification, the growth of Vallisneria natans (V. natans), and microbial mechanisms were explored through SFCW simulation experiments. The results showed that through the joint action of biochar and V. natans, the concentrations of total nitrogen, total phosphorus, and ammonia nitrogen in the effluent significantly decreased. The total biomass, relative growth rate, and chlorophyll content of V. natans were significantly reduced by adding biochar (≥20%, v/v), as the root activity and the root to leaf biomass ratio slightly increased at first and then decreased. The carbon and nitrogen contents of V. natans slightly increased with the addition of biochar (≥10%, v/v), but the phosphorus content slightly decreased. Moreover, the nitrogen content of the matrices decreased significantly over time (P<0.05), and the phosphorus content in the matrix showed an increasing trend in the same period. In addition, the microbial 16S rDNA sequencing results indicated that the diversity and abundance of the microbial community in the matrix of the biochar-added SFCW tended to decrease. Nevertheless, the abundance of functional bacteria related to nitrogen and phosphorus removal (i.e., Pseudomonas and Dechloromonas) slightly increased, which would benefit denitrification and dephosphorization in the SFCW. Hence, the addition of biochar to the SFCW matrix facilitated the improvement of effluent water quality, while excessive biochar addition (≥10%, v/v) restrained the growth of V. natans but did not cause death. This conclusion provides valid data support regarding the ability of biochar-added SFCW to purify lightly contaminated water.

Combining chlor(am)ine-UV oxidation to ultrafiltration for potable water reuse: Promoted efficiency, membrane fouling control and mechanism

Wastewater reuse has been progressively popular as a practical method for protecting aquatic environment and water sources. In this work, the chlor(am)ine-UV oxidation was employed to enhance membrane system performance during potable water reuse. The achievements were comprehensively evaluated from the aspects of membrane fouling mitigation and organic matter removal. The various dosages of chlorine and UV irradiation were applied and the effects of typical inorganic species in wastewater effluent were considered as well. It was suggested that the chlor(am)ine-UV oxidation could significantly promote the normalized flux by 94.9% under the condition of 10 mg L-1/960 mW cm-2 (chlorine dose and UV irradiation density). And the certain lower concentration of inorganic pollutant in wastewater effluent could further prevent the membrane fouling accumulation, especially for the reversible and total fouling resistances. The model fitting of filtration flux revealed that the combination of pore blockage and cake filtration was responsible for the mechanisms of fouling formation, and the transition moment was adjusted by the oxidation process. The characteristics of dissolved organic matter were modified as well, which were positive for the improvement of membrane effluent quality and security. The results demonstrated that the combination of the chlor(am)ine-UV oxidation and ultrafiltration could be a promising alternative for efficient wastewater recycle and reuse.

Coupled microalgal–bacterial biofilm for enhanced wastewater treatment without energy investment

In view of water-resource depletion, treated wastewater can serve as an alternative source for crop irrigation. However, conventional wastewater-treatment plants are energy-intensive and costly to construct and operate, especially for lower middle-income countries. The present study focused on improving the quality of wastewater by incorporating a coupled microalgal–bacterial biofilm (CMBB) treatment in wastewater ponds. Standard polyether sponges were dipped in raw wastewater samples to enhance biofilm development on them. The enriched sponges were used to treat wastewater, with or without external energy for aeration. Wastewater parameters were analyzed during the enrichment and treatment processes. The CMBB technology and aeration resulted in similar improvement of effluent quality, but the former saved on energy costs, and reduced total chemical oxygen demand (COD) by 36 % within 24 h and 71 % within 4 days; the values of biochemical oxygen demand (BOD), ammonium and phosphates decreased by 80 %, 64 % and 95 %, respectively, within 7 days. The resultant COD and BOD values were below the maximum allowed for reuse and discharge.

Application of potassium ferrate combined with poly-aluminum chloride for mitigating ultrafiltration (UF) membrane fouling in secondary effluent: Comparison of oxidant dosing strategies

Coagulation has been widely applied as a pretreatment for ultrafiltration (UF) membrane in wastewater reclamation, however, it is unable to effectively ensure the removal of organic micropollutants (OMPs) and genotoxicity. To solve this problem, oxidant ferrate (VI) (FeVIO42−, FeVI) was combined with coagulant poly-aluminum chloride (PAC) as the pretreatment of UF to treat secondary effluent, and three oxidant dosing strategies (namely oxidation followed by coagulation (O–FeVI-PAC), simultaneous oxidation and coagulation (S–FeVI-PAC), and coagulation followed by oxidation (C-PAC-FeVI)) were compared at two oxidant doses. The results showed that C-PAC-FeVI pretreatment exhibited the best performance for the removal of DOC (35.9%), UV254 (33.7%), protein (71.8%), and polysaccharide (22.1%). Molecular weight and fluorescence analysis revealed that the removed organics were mainly humic substances. Both the direct UF process and PAC pretreatment showed limited removal of OMPs and genotoxicity, however, the combined pretreatments of FeVI and PAC dramatically removed them. The maximum removal efficiency of the fourteen selected OMPs and genotoxicity was obtained under S–FeVI-PAC (59.6% on average) and C-PAC-FeVI (84.1%), respectively. With respect to membrane fouling control, the normalized flux reduction showed an apparent regularity of C-PAC-FeVI > O–FeVI-PAC > S–FeVI-PAC, however, FeVI dose should be carefully determined. The addition of FeVI delayed the transition of membrane fouling mechanism from pore blockage to cake filtration, especially in C-PAC-FeVI pretreatment, which was confirmed by the fluorescence characterization of hydraulic reversible and hydraulic irreversible foulants. To sum up, C-PAC-FeVI dosing strategy seems to have more potential in membrane fouling alleviation and effluent quality improvement.

Supervisory control configurations design for nitrogen and phosphorus removal in wastewater treatment plants.

Model predictive control (MPC) and Fuzzy controllers are designed in a two-level hierarchical supervisory control framework for control of activated sludge-based wastewater treatment plants (WWTP) in order to efficiently remove nitrogen and phosphorus. Benchmark simulation model No.3 with a bio-phosphorus (ASM3bioP) module is used as a working platform. The hierarchical control framework is used to alter the dissolved oxygen in the seventh reactor (DO7 ) to control ammonia. Lower-level PI, MPC, and Fuzzy are used to control the nitrate levels in the fourth reactor (SNO4 ) by manipulating internal recycle (Qintr ) and DO7 in the seventh tank by manipulating mass transfer coefficient (KL a7 ). MPC and Fuzzy are designed in the supervisory layer to alter the DO7 set-point based on the ammonia composition in the seventh reactor (NH7 ). From the analysis, it is observed that the effluent quality is improved with a decrease in ammonia, TN, and TP. Though a little difference was observed in the cost for all the control strategies, a trade-off is maintained between cost and percentage improvement of effluent quality. MPC-MPC combination showed significant removal in ammonia and better effluent quality when compared to other control strategies. PRACTITIONER POINTS: Developed novel strategies in hierarchical configurations for better nutrient removal with optimal costs in an A2 O process. Lower level control strategies deals with dissolved oxygen in last aeration tank and nitrate in fourth anoxic tank (PI/MPC) Higher level control strategy deals with ammonia in the last aeration tank (MPC/Fuzzy). Average and violations of nutrient removal, economy and overall effluent quality for three weather conditions (Dry, Rain and Strom) are studied. A trade-off is observed between EQI and OCI.