Biological Wastewater Treatment Processes Research Articles

Comparing biotransformation of extracellular polymeric substances (EPS) under aerobic and anoxic conditions: Reactivities, components, and bacterial responses

This study aimed to better understand the transformation behaviors of extracellular polymeric substances (EPS) and their roles in regulating bacterial community in biological wastewater treatment processes. Herein, well-controlled bioassays under aerobic and anoxic conditions were performed to investigate degradation dynamics, composition variations, and bacterial response during EPS transformation. Reactivity continuum modeling showed that organic pools of EPS had continuous reactivity distributions, and most labile organic fraction with a degrading rate >0.1 h−1 was substantially higher under aerobic (20.47%) than anoxic (2.02%) condition. Rapid degradation of protein-like substances in the initial degradation stage was accompanied by the humification process, as revealed by UV absorption spectroscopy, fluorescence spectroscopy, and size exclusion chromatography with continuous organic carbon detection analysis. The 16S rRNA gene sequencing results showed that the selection effect of EPS in controlling abundant populations during their transformation, e.g., Acinetobacter was enriched, and Candidatus Competibacter was washed out relative to the source community. Furthermore, taxonomic normalized stochasticity ratio-based null model and bacterial ecological network analysis indicated higher relative importance of deterministic process in shaping the EPS-degrading communities under aerobic than anoxic condition, likely explaining the faster EPS biotransformation under aerobic condition. Intriguingly, the keystone populations driving EPS metabolism showed the environmental filtering characteristics (e.g., capable of degrading refractory and aromatic compounds or adapting to harsh environments) and cooperative interactions with the co-occurring species under both conditions. This work is expected to reveal the fates and roles of EPS in wastewater treatment plants extensively.

Long-term evaluation of the effect of peracetic acid solution on anaerobic wastewater treatment: Process performance and microbial community structure

Peracetic acid (PAA) has been extensively used in poultry processing as an effective disinfectant. However, PAA-bearing poultry processing wastewater can lead to severe upsets of biological wastewater treatment processes. The objective of this study was to assess the long-term effect of PAA solution (PAA and hydrogen peroxide, H2O2) on the anaerobic treatment of poultry processing wastewater. Five reactors were operated for 177 d, semi-continuously fed with poultry processing wastewater and gradually increased levels of H2O2 or PAA solution, added either to the wastewater before feeding (indirect addition), or to the reactors immediately after feeding (direct addition). Indirect, well pre-decomposed H2O2 and PAA had limited effect on biogas production and COD destruction. Biogas production was completely inhibited with direct addition of H2O2 at 227 mg/L, but recovered in ca. 2 d. Direct addition of PAA solution at 500/100 mg/L PAA/H2O2 completely inhibited biogas production and required ca. 18 d incubation for recovery. Methanogenesis was more impacted than fermentation. Long-term H2O2 or PAA solution addition led to a relatively low shift in both bacterial and archaeal communities. The major methanogenic orders were Methanosarcinales and Methanomicrobiales. Direct PAA solution addition decreased both acetoclastic and hydrogenotrophic methanogenic activity; acetoclastic methanogenesis was affected the most.

Insight into the interaction between trimethoprim and soluble microbial products produced from biological wastewater treatment processes

Soluble microbial products (SMPs), dissolved organic matter excreted by activated sludge, can interact with antibiotics in wastewater and natural water bodies. Interactions between SMPs and antibiotics can influence antibiotic migration, transformation, and toxicity but the mechanisms involved in such interactions are not fully understood. In this study, integrated spectroscopy approaches were used to investigate the mechanisms involved in interactions between SMPs and a representative antibiotic, trimethoprim (TMP), which has a low biodegradation rate and has been detected in wastewater. The results of liquid chromatography-organic carbon detection-organic nitrogen detection indicated that the SMPs used in the study contained 15% biopolymers and 28% humic-like substances (based on the total dissolved organic carbon concentration) so would have contained sites that could interact with TMP. A linear relationship of fluorescent intensities of tryptophan protein-like substances in SMP was observed (R2>0.99), indicating that the fluorescence enhancement between SMP and TMP occurred. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that carboxyl, carbonyl, and hydroxyl groups were the main functional groups involved in the interactions. The electrostatic and π-π interactions were discovered by the UV-vis spectra and 1H nuclear magnetic resonance spectra. Structural representations of the interactions between representative SMP subcomponents and TMP were calculated using density functional theory, and the results confirmed the conclusions drawn from the 1H nuclear magnetic resonance spectra. The results help characterize SMP–TMP complexes and will help understand antibiotic transformations in wastewater treatment plants and aquatic environments.

Differences in sensitivity of human lymphocytes and fish lymphocytes to polyvinyl chloride microplastic toxicity.

Polyvinyl chloride (PVC) microplastics are emerging contaminants affecting biological wastewater treatment processes. So far, the toxicological investigation of PVC microplastics usually focused on the anaerobic and denitrifying bacteria. It seems that the primary lymphocytes isolated from peripheral blood are more sensitive than most other organ cell types in vitro; therefore, the aim of this study was to assess the cytotoxicity of PVC microplastic on human and fish blood lymphocytes as a useful ex vivo model for accelerated human toxicity studies. Using biochemical analyses, we showed human lymphocytes are more sensitive to toxic effects of PVC microplastic than fish lymphocytes. Our result showed that addition of PVC microplastic at 24, 48, and 96μg/ml for 3h to human blood lymphocytes induced cytotoxicity. The PVC microplastic-induced cytotoxicity on human blood lymphocytes was associated with intracellular reactive oxygen species (ROS) formation, lysosomal membrane injury, mitochondrial membrane potential (MMP) collapse, depletion of glutathione, and lipid peroxidation. According to our results, PVC microplastic particles induce oxidative stress and organelle damage in human lymphocytes, while these significant alterations in toxicity parameters in PVC microplastic-treated fish lymphocytes were not observed. Finally, our findings suggest that human lymphocytes are more sensitive to PVC microplastic toxicity compared with fish lymphocytes.

Heavy metals and polycyclic aromatic hydrocarbons in leachates from autothermal thermophilic aerobic digestion as a potential threat to the environment in north-eastern Poland

This paper presents the concentrations of the polycyclic aromatic hydrocarbons (PAH) and heavy metals in leachates from the autothermal thermophilic aerobic digestion (ATAD). The leachates from ATAD installations (Dąbrowa Białostocka, Hajnówka, Pisz, Olecko, Giżycko, Wysokie Mazowieckie) located in Poland were tested. The concentrations of PAHs in samples from Pisz, Giżycko, Wysokie Mazowieckie and Hajnówka were similar to those in industrial wastewater. The cluster analysis confirmed that in sites with a higher polyethylene (p.e.) input from the industrial sector, the leachates were more contaminated with PAH compounds. In samples from Dąbrowa Białostocka, Olecko, Pisz and Hajnówka, the heavy fraction of PAHs compounds prevailed over the light fraction. Concentrations of heavy metals in leachates from ATAD varied. The Ward’s method isolated the wastewater treatment plant in Giżycko. The p.e. from the industrial sector was the highest for this facility. Also, the samples from ATAD had the highest total concentration of heavy metals (5.87 mg/l). The leachates from ATAD are returned to biological systems of municipal sewage treatment plants, where they can be combined into more toxic compounds. Biological wastewater treatment processes do not ensure the removal of PAHs and heavy metals from the wastewater. As a result, harmful compounds can get into the water or ground, polluting the environment.

GAC Adsorption of Dissolved Organic Matters for CSOs Treatment and Bioregeneration of Spent-GAC Using Denitrification

The capability of a laboratory-scale reactor packed with granular activated carbon (GAC) was evaluated in the removal process of organic matter dissolved in Combined Sewer Overflows (CSOs). First, the capacity of adsorption was recorded by six types of organic matter passing through the GAC reactor. Second, the breakthrough period was investigated when the CODcr adsorption ratio fell below 30% by varying the input intensity of CODcr into the GAC reactor from high, medium, to low. Lastly, the possibility of regenerating GAC through the denitrification process was examined. As a result, GAC adsorption capacity was ranked in order of sewage > sodium acetate > methanol > LB broth ≒ Glucose. Uniquely, glucose, being easily removed in the biological wastewater treatment process, had a low GAC adsorption capacity in this process. Thus, GAC showed the best adsorption for sewage among tested organic matters. Secondly, the breakthrough periods of the GAC adsorption reactor were 21, 28, and 32 days under high, medium, and low CODcr conditions, respectively. Lastly, the organic matter adsorbed in the GAC micro-pore was reused as an external organic carbon source to denitrifying bacteria in CSOs. However, the re-adsorption capacity was not at a satisfactory level which needs further research.

The short- and long-term effects of cold-temperature shock on partial nitritation - improved assessment methodology

This research sheds light on the gap in knowledge concerning the effect of temperature shock on nitrifiers. This phenomenon was analysed in context of mainstream bioaugmentation with nitrifiers cultivated in a sidestream partial nitritation process, which was recently experimentally confirmed to be beneficial in municipal wastewater treatment plants. In this study, using respirometric activity measurements and a simple mathematical model of nitritation, it has been proven that fluctuations in nitrifier concentration in long term tests affect the value of the estimated temperature correction coefficient (θ). Furthermore, this leads to underestimation of its value and thus, results in inaccurate prediction of the scale of the temperature shock effect. During the first days following the shock occurrence, the estimated process rate using the new approach was equal to only 64.1 ± 9.7% of the value calculated using previously preferred methods. Moreover, faster biomass acclimatisation to lower temperature in the following days was observed. These observations clearly indicate the need for change in the current approach and confirm the validity of the proposed improvements. It can be assumed, that the presented insights concerning the method of temperature effect assessment are transferrable to other microbial communities involved in biological wastewater treatment processes.

Revealing the effects of static magnetic field on the anoxic/oxic sequencing batch reactor from the perspective of electron transport and microbial community shifts

The effects of static magnetic field (SMF) on an anoxic/oxic sequencing batch reactor were investigated from the perspective of electron transport via determining the variations of reduced/oxidized nicotinamide adenine dinucleotide (NADH/NAD+) ratio, NADH concentration, electron transport system activity (ETSA), poly-β-hydroxybutyrate (PHB), extracellular polymeric substances (EPS), as well as the gene expression under different conditions. Moreover, the shifts of microbial community were also analyzed. The application of SMF with an appropriate intensity significantly improved the performance of the process, the abundance of the anoxic denitrifiers, and the activity of the aerobic denitrifiers. The NADH content, as well as ETSA were also enhanced, therefore, the total nitrogen removal efficiency of the process was increased. However, the overhigh SMF intensity resulted in the change of microbial community, meanwhile, had negative effects on the metabolism of microorganisms. Selecting a proper intensity is crucial for the SMF-enhanced biological wastewater treatment process.

Determination of the Optimal Parameters of the Jet Aeration

To ensure effective aeration of the biological wastewater treatment process, easy-to-operate and not too energy-intensive units are needed. Jet aerators have such capabilities. In this study, the authors searched for the best hole shape for the aeration nozzles. It was determined that a nozzle with an elongated hole has the largest size of the actively aerated zone. Experimental studies of nozzles of a diameter of 56 mm with nozzles of elongated shape showed that the best characteristics of mass transfer are provided by nozzles with a total area of holes of 356 mm2 at a flow rate of 10 … 12 m/s. For practical calculations, an equation was obtained for the dependence of the oxygen transfer coefficient KLa(20) on the complex criterion vn, and a method for calculating aeration units was developed, which is applicable for aerators with elongated holes.

Potential of Bacterial Strains Isolated from Coastal Water for Wastewater Treatment and as Aqua-Feed Additives.

Bacteria have various and sustained effects on humans in various fields: molecular biology, biomedical science, environmental/food industry, etc. This study was conducted to evaluate the wastewater treatment capacity and feed-additive fish-growth effect of four strains of bacteria: Pseudoalteromonas mariniglutinosa, Psychrobacter celer, Bacillus albus, and Bacillus safensis. In a wastewater degradation experiment, (i) nitrate-N and nitrite-N were removed within 1 h in all of the 4 bacterial strains; (ii) the removal rates of TAN and TN were higher in all of the strains relative to the B. subtilis. In a feed-additive experiment (5% Kg−1), (i) the growth of fish was higher in all of the 4 bacterial strains with the B. subtilis relative to the commercial feed; (ii) there was no significant growth difference for B. albus and B. safensis relative to the B. subtilis, but growth was higher in P. mariniglutinosa and P. celer. The results indicated that the 4 bacterial strains can be effectively utilized for biological wastewater treatment processes and as aqua-feed.

High-gravity technology-enhanced activated sludge process for municipal wastewater treatment

Aerobic activated sludge process (AAS) is the most widely used biological wastewater treatment process, and its treatment efficiency is affected by dissolved oxygen (DO) concentration and mass transfer rate. Herein, high-gravity technology (Higee), an efficient mass transfer enhancement technique, was used to enhance AAS to improve municipal wastewater treatment efficiency. Compared with AAS, AAS enhanced by Higee (Higee-AAS) shortened the time to reduce chemical oxygen demand and NH3-N to below the discharge limits by 1/3 and 3/5, respectively. The removal efficiency of aliphatic/proteins by Higee-AAS is about 4 times that of AAS. Intensification mechanisms were revealed from the changes of DO concentration, sludge morphology, and microbial activity. DO increased dramatically, and activated sludge became more dispersed with smaller particle size, which facilitated contact between oxygen and sludge, improving oxygen utilization rate and microbial activity. This study provides a basis for the application of Higee-AAS on an industrial scale.

Electrochemical Valorization of Waste Activated Sludge for Short-Chain Fatty Acids Production

During the wastewater biological treatment process, a significant amount of waste activated sludge (WAS) is produced, which must be properly treated before disposal. The cost of WAS disposal accounted for nearly 50–60% of a wastewater treatment plant’s operating costs. The disposal of a large amount of WAS has become a serious environmental and economic problem as wastewater treatment capacity has increased. Furthermore, WAS has been considered as a sustainable resource due to a high organic matter content (>40%, mainly proteins, and carbohydrates) with an average calorific value of 6094 kcal/kg. As a result, harnessing bioenergy from WAS could resolve both environmental and economic issues raised by the growing amount of WAS.The intermediate chemicals in anaerobic digestion are short-chain fatty acids (SCFAs) (e.g., acetic acid, propionic acid, butyric acid, etc.). SCFAs are more beneficial (600-3815$/ton) than biogas (150$/ton) and produced in a shorter period (less than 2d). SCFAs production from waste activated sludge is getting popular in wastewater treatment plants (WWTPs) because SCFAs can be used for a variety of applications, including biohydrogen production, bioplastics (polyhydroxyalkanoate (PHA), and biological nutrient removal.Electrochemical treatment has been shown to be a powerful and environmentally friendly method of disrupting sludge floc and sludge disintegration to create SCFAs by oxidizing complex organic compounds on the electrode surface. On the other hand, the alkaline pH is more favorable for protein and carbohydrate destruction which results in a substantial increase in SCFAs production. Furthermore, methanogenesis reactions are mitigated in alkaline media, so that more SCFAs accumulate as a final product.In this study, the electrochemical treatment under an alkaline environment was utilized in a single chamber electrolysis cell at low operating temperatures (25-55 °C) to achieve solid reduction and SCFAs production. The effect of the operating condition such as applied potential, electrode materials, operating temperature, and alkaline agent concentration on SCFAs production was investigated. The waste activated sludge solid before and after treatment was characterized by thermogravimetric analysis (TGA), Scanning electron microscope (SEM), and elemental analysis techniques. The supernatant liquid after electrochemical treatment was evaluated with gas chromatography- flame ionization detector (GC-FID) to analyze the SCFAs concentration. In this presentation, the results from this research study will be provided including volatile solid removal, SCFAs concentration, and solid residue characterization.

Effect of biofilm media application on biomass characteristics and membrane permeability in the biological spatiotemporal phase-separation process

In this study, the effect of moving-bed biofilm carrier, a membrane, and simultaneous employment to solve the settleability problem derived from readily biodegradable organics application in the biological spatiotemporal phase separation and variation of biomass characteristics by biofilm media application were investigated. No significant differences of the treatability among each case were observed. Although the moving-bed biofilm process is commonly used for the treatment of organics and nitrogen in wastewater, phosphorus was also removed perfectly owing to the detached biomass containing orthophosphate was discarded sufficiently. Additionally, the concentration of the suspended biomass decreased significantly, and the settled volume index was improved dramatically from 700 to 100 mL/g after the addition of the biofilm carrier. Although the extracellular polymeric substance (EPS) concentration increased with media addition, the back-flushing interval of the membrane was lengthened. The increment of polysaccharide in the EPS and the non-existence of protein in the soluble EPS were clearly observed. Thus, the suspended-biomass decrement due to media addition and the protein concentration in the EPS played important roles for fouling control. This study provides valuable information on state alternation of biomass by biofilm media application on biological suspended growth wastewater treatment process.

Fouling and mitigation mechanisms during direct microfiltration and ultrafiltration of primary wastewater

Direct membrane filtration (DMF) has recently gained attention as an alternative secondary biological wastewater treatment process. This study evaluated direct microfiltration (MF) and ultrafiltration (UF) performance and cleaning protocols during crossflow DMF of primary municipal wastewater effluent. Several types of MF and UF membranes were examined by threshold flux determination, and two types of membranes (MF, 0.08 μm; UF, 100 kDa) were chosen for exploring membrane fouling mechanisms at different feed pressures via both fouling resistance analysis and optical coherence tomography (OCT) observation. The results revealed that both MF and UF displayed three-stage fouling behaviors, i.e., initial intermediate pore blocking followed by two-stage cake filtration. Increasing feed pressure from 8 kPa to 50 kPa could accelerate physically reversible fouling rate (consistent with simulated cake filtration constant). During physical flushing, the cake layer was more readily removed from the UF membrane; while residual porous cake layer was present on the MF membrane, regardless of the feed pressure. With extending filtration-cleaning cycle, shortening filtration duration and elevating cleaning solution temperature to from 25 °C to 50 °C benefited for irreversible fouling alleviation. At 50 °C, the geothermal water performed similar cleaning behaviors as clean water, facilitating lower reversible and irreversible fouling than the geothermal brine. This study shed light on the feasibility of using high temperature geothermal water for periodic physical cleaning during DMF of wastewater under Icelandic scenario.

Sustained and enhanced anaerobic removal of COD and nitrogen in a zeolite amended glycogen accumulating organism dominated biofilm process

Activated sludge, the most widely used biological wastewater treatment process is known to be expensive to operate, largely due to energy expense for oxygen transfer into the bulk wastewater solution. The alternative of using passive aeration facilitates oxygen supply directly from the air resulting in aeration energy savings. The current study demonstrated sustained and improved removal of chemical oxygen demand (COD) and nitrogen in a zeolite modified glycogen accumulating organisms (GAOs) dominated biofilm reactor, which achieved anaerobic removal of COD and ammonium by the activity of GAOs and zeolite, respectively. Draining of the batch-operated reactor enabled the biofilm to directly uptake oxygen from air (passive aeration) to carry out simultaneous nitrification and denitrification due to the activity of GAO (Candidatus competibacter) and nitrifying bacteria (Nitrosomonas and Nitrospira). Under stable long-term (4-months) operation, the process achieved COD and nitrogen removal at rates of 1354 and 79.1 g m−3 d−1, respectively. The biofilm process demonstrated >90% nitrogen removal efficiency in multi-cycle (4/8 cycles) strategy with a short treatment time of 8 h. Due to the passive aeration scheme, the energy consumption of the proposed wastewater treatment process is calculated to be about 13-times less than that of traditional activated sludge process. Therefore, the Passive Aeration Simultaneous Nitrification and Denitrification (PASND) biofilm process is a promising low-energy treatment step for efficient removal of COD and nitrogen from wastewater.

Biodiesel production of Rhodosporidium toruloides using different carbon sources of sugar-containing wastewater: Experimental analysis and model verification

Wastewater containing chemical energy and water resources is supposed to be efficiently recovered and utilized. However, conventional wastewater treatment, which is energy intensive and costly, focuses on the degradation of pollutants but ignores the reuse of resources. This study explored the feasibility of integrating wastewater treatment with biofuel production by oleaginous yeasts Rhodosporidium toruloides for sustainability concerns. Aerobic fermentation of R. toruloides was used to treat synthetic sugar-containing wastewater (SSCW) and synthetic sugar-containing wastewater anaerobic fermentation broth (SSCW-AFB). Flux balance analysis (FBA) was used to explore the optimal metabolic flux distributions for lipid production, and the potential of R. toruloides to utilize acetic acid was studied through metabolic network analysis for the first time. Sequencing batch cultivation was used to enhance nutrient removal and microbial lipid accumulation, achieving 87.0 ± 2.4% and 61.0 ± 0.1% total organic carbon (TOC) removal coupled with 30.6 ± 1.1% and 73.5 ± 0.7% lipid content in SSCW and SSCW-AFB, respectively. The in silico results revealed that nicotinamide adenine dinucleotide phosphate (NADPH)-producing flux of R. toruloides grown on acetic acid preferred going through malic enzyme related pathways rather than the pentose phosphate pathway, resulting in less 15.6% CO2 emissions which in turn facilitates the lipid accumulation. Consistent with the model predictions, a higher lipid coefficient (147.0 mg/g acetic acid) was achieved in SSCW-AFB compared with that in SSCW (105.3 mg/g glucose) during the bioprocess. Furthermore, the lipid production performance under a low seed cell density (0.4 g/L) was significantly better than that under a high seed cell density (4 g/L). Analysis of the biofuel properties indicated the suitability of using SSCW and SSCW-AFB as feedstocks for the industrial production of biodiesel. The results of this study provide valuable information for promoting resource and energy recovery and reducing carbon emission during the wastewater biological treatment process by oleaginous microorganisms.

Extracellular electron transfer via multiple electron shuttles in waterborne Aeromonas hydrophila for bioreduction of pollutants.

Members of the genus Aeromonas prevail in aquatic habitats and have a great potential in biological wastewater treatment because of their unique extracellular electron transfer (EET) capabilities. However, the mediated EET mechanisms of Aeromonas have not been fully understood yet, hindering their applications in biological wastewater treatment processes. In this study, the electron shuttles in Aeromonas hydrophila, a model and widespread strain in aquatic environments and wastewater treatment plants, were explored. A. hydrophila was found to produce both flavins and 2-amino-3-carboxy-1,4-naphthoquinone (ACNQ) as electron shuttles and utilize them to accelerate its EET for the bioreduction of various pollutants. The Mtr-like respiratory pathway was essential for the reduction of flavins, but not involved in the ACNQ reduction. The electron shuttle activity of ACNQ for pollutant bioreduction involved the redox reactions that occurred inside the cell. These findings deepen our understanding about the underlying EET mechanisms in dissimilatory metal reducing bacteria and provide new insights into the roles of the genus Aeromonas in biological wastewater treatment.

Multi-Integrated Systems for Treatment of Abattoir Wastewater: A Review

Biological wastewater treatment processes such as activated sludge and anaerobic digestion remain the most favorable when compared to processes such as chemical precipitation and ion exchange due to their cost-effectiveness, eco-friendliness, ease of operation, and low maintenance. Since Abattoir Wastewater (AWW) is characterized as having high organic content, anaerobic digestion is slow and inadequate for complete removal of all nutrients and organic matter when required to produce a high-quality effluent that satisfies discharge standards. Multi-integrated systems can be designed in which additional stages are added before the anaerobic digester (pre-treatment), as well as after the digester (post-treatment) for nutrient recovery and pathogen removal. This can aid the water treatment plant effluent to meet the discharge regulations imposed by the legislator and allow the possibility for reuse on-site. This review aims to provide information on the principles of anaerobic digestion, aeration pre-treatment technology using enzymes and a hybrid membrane bioreactor, describing their various roles in AWW treatment. Simultaneous nitrification and denitrification are essential to add after anaerobic digestion for nutrient recovery utilizing a single step process. Nutrient recovery has become more favorable than nutrient removal in wastewater treatment because it consumes less energy, making the process cost-effective. In addition, recovered nutrients can be used to make nutrient-based fertilizers, reducing the effects of eutrophication and land degradation. The downflow expanded granular bed reactor is also compared to other high-rate anaerobic reactors, such as the up-flow anaerobic sludge blanket (UASB) and the expanded granular sludge bed reactor (EGSB).

The circulating fluidized bed bioreactor as a biological nutrient removal process for municipal wastewater treatment: Process modelling and costing analysis

Emerging technologies for wastewater treatment face an uphill battle to be adopted in practice because no large-scale costing data exists to prove their cost competitiveness. Similar technologies and their costing data offer some insight to the approximate cost, but more detailed estimates are required for a final decision on process selection. The circulating fluidized bed bioreactor (CFBBR) is one such technology, proven at the lab and pilot and scale, but is yet to be used on a large scale. In order to demonstrate the potential economic competitiveness of the CFBBR, a method of modifying the CapdetWorks costing software by first modeling the CFBBR in the GPS-X process simulation software was employed. The modelling was used to determine the necessary changes to a moving bed bioreactor (MBBR) process (media size, density, surface area, and bed fill fraction) in CapdetWorks to simulate the CFBBR and then generate costing estimates for both capital cost (CapEx) and operation and maintenance cost (OpEx). Benchmarking the cost estimates against simulations of conventional suspended and attached growth processes and external costing data from the US EPA was performed to both validate the costing method and analyze the CFBBR's economic competitiveness. The calculation of the net present value from the CapEx and OpEx showed that the CFBBR is predicted to have 10%–30% lower costs at low flows of 1.5 and 4.6 MGD and comparative costs to conventional processes at higher flows from 10 to 30 MGD. Furthermore, the smaller land footprint of the CFBBR-based plants and lower landfilled biosolids implies that the CFBBR's environmental footprint is superior to its competitors and offers advantages for both small-sized plants and large urban plants.

PH-dependent biological sulfidogenic processes for metal-laden wastewater treatment: Sulfate reduction or sulfur reduction?

Both biological sulfate reduction process and sulfur reduction process are attractive technologies for metal-laden wastewater treatment. However, the acidity stress of metal-laden wastewater could affect the sulfidogenic performance and the microbial community, weaken the stability, efficiency and cost-effectiveness of the biological sulfidogenic processes (BSP). In this study, long-term lab-scale trials were conducted with a sulfate-reducing bioreactor and a sulfur-reducing bioreactor to evaluate the effects of acidity on sulfidogenic activities and the microbial community of the BSP. In the 300-day trial, the sulfate-reducing bacteria (SRB)-driven BSP was stable in terms of sulfidogenic performance and microbial community with the decline of pH, while the sulfur-reducing bacteria (S0RB)-driven BSP achieved high-rate and low-cost sulfide production under neutral conditions but unstable under acidic conditions. With the decline of pH, the sulfide production rate (SPR) of the SRB-driven BSP stably increased from 30 to 83 mg S/L-h; while it decreased from 56 to 37 mg S/L-h in the S0RB-driven BSP with high fluctuation. The results of estimation were consistent with the thermodynamical calculations, in which the sulfur reduction process showed a better performance at pH 5–7, while the sulfate reduction process might gain more energy when pH<5. The stable sulfidogenic performance and microbial community diversity of the SRB-driven BSP could be attributed to the alkalinity produced in sulfate reduction to buffer the acidic stress. In comparison, the microbial community in the S0RB-driven BSP was significantly re-shaped by acidity stress, and the predominant sulfidogenic bacterium changed from Desulfovibrio at neutral condition, to Desulfurella at pH≤5.4. The stability of the microbial community significantly affected the SPR and the operational cost. Nevertheless, the organic consumption for sulfide production of the S0RB-driven BSP was still less than the SRB-driven BSP even in acidic conditions. Collectively, the S0RB-driven BSP was recommended under neutral or mild acid conditions, while the SRB-driven BSP was more suitable under fluctuating pH conditions, especially at low pH. Overall, this study presented the long-term performance of SRB- and S0RB-driven BSP under varying pH conditions, and provided guidance to determine the suitable BSP and operational cost for different metal-laden wastewater.