Synthetic Domestic Sewage Research Articles

Coagulation performance and floc characteristics of Fe–Ti–V ternary inorganic coagulant for organic wastewater treatment

A novel Fe–Ti–V ternary inorganic coagulant (VTMS) was prepared from vanadium titanomagnetite (VTM) by two-step sulfuric acid leaching method, which is simple, efficient, and economical. VTMS was used to treat four typical organic wastewaters: synthetic domestic sewage, oily wastewater, surface water, and algae-laden water. The results indicated that it was superior to conventional coagulants. VTMS achieved a turbidity removal rate of nearly 100 % for all four wastewaters. In addition, it performed better in organic matter removal than polyaluminum chloride (PAC) with a larger floc size and higher growth rate. These results were attributed to the hydrolysis of Fe, Ti, and V, which formed a chain structure that improved the adsorption, bridging, and sweeping performances of VTMS. Based on the observations of coagulation performance, floc properties, and zeta potential, the predominant coagulation mechanisms appeared to be charge neutralization in synthetic domestic sewage and bridging flocculation in oily wastewater, surface water, and algae-laden water. Sweep coagulation also played a role in the coagulation processes for all four wastewaters. This study provided efficient technical guidance for large-scale production and application of Ti-based coagulants.

Development of a low-cost electrochemical sensor for monitoring components in wastewater treatment processes

ABSTRACT Anaerobic digestion (AD) is a complex biological process widely used to decompose various types of organic matter, as well as to produce some metabolites and biogas. Diverse microorganism groups cooperate in many intricate metabolic routes so that organic matter can be degraded. However, any imbalance on these routes can lead to process instability or even failure. Therefore, a proper monitoring system, as well as a good understanding of the process, are key steps to improve performance and stability. Several mathematical models have been developed to represent AD. Despite this, process monitoring is mostly conducted by analytical methods, whose equipment is either expensive or the analyses are time-consuming, which may be a hindrance to low-budget developments. The objective of this study was to develop a low-cost electrochemical sensor to monitor components in wastewater treatment plants. Hundreds of synthetically supplemented sugarcane vinasse and synthetic domestic sewage samples were characterised. The obtained signals were used to calibrate principal component regression, partial least square and artificial neural network estimation models. The predictable variables were chemical oxygen demand, volatile fatty acids, sodium bicarbonate, beef extract, and lipids, and their R2 ranged from 0.84 to 0.99, depending on the component.

Toilet paper and food waste in UASB reactors: A contribution to reducing the amount of conventional solid waste disposal

AbstractThe release of toilet paper (TP) and food waste (FW) in domestic sewage is a common practice in developed countries. Nevertheless, this practice has started to be used in developing countries where anaerobic digestion is applied. Therefore, this work aimed at evaluating the influence of the presence of TP and FW on the anaerobic digestion process in UASB reactors. During the experiment, two UASB reactors (8L) were fed with synthetic domestic sewage with the addition of toilet paper (TPR) and food waste (FWR) residues, respectively. In the first stage of the experiment (S‐I), the reactors operated with an organic load of 0.97 kg COD.m–3.d–1 (TPR) and 0.96 kgCOD.m–3.d–1 (FWR) and, in the second stage (S‐II), the quantities were increased to 1.58 kgCOD.m–3.d–1 (TPR) and 1.35 kgCOD.m–3.d–1 (FWR). In the experimental period of 110 days, the parameters total and filtered COD, series of solids, pH, alkalinity, and VFA were monitored. The mean removal of total COD was of 79±1% (S‐I) and 75±1% (S‐II) for TPR, and of 81±2% (S‐I) and 76±1% (S‐II) for FWR. Regarding VSS, the mean removal was of 94 ± 2% (S‐I) and 97 ± 1% (S‐II) for TPR, and of 95 ± 3% (S‐I) and 96 ± 1% (S‐II) for FWR. The VFA/TA ratio increased from S‐I (0.03 for TPR and FWR) to S‐II (0.17 to TPR and 0.10 to FWR), responding to the organic load increases, but still in the range of process stability. The added toilet paper or food waste were efficiently removed in both stages, reaching removals higher than 75%. In general, both reactors presented a good performance for the anaerobic process even under changes in organic load and influent composition. This experiment showed the feasibility of the combined treatment of TP or FW with domestic sewage in UASB reactors.

Combined effects of electrical current and nonsteroidal antiinflammatory drugs (NSAIDs) on microbial community in a three-dimensional electrode biological aerated filter (3DE-BAF)

Three-dimensional electrode biological aerated filter (3DE-BAF) with particulate bioelectrode from lithium slag was used to simultaneously remove diclofenac and clofibric acid from the synthetic domestic sewage, and the combined effects of electrical current and nonsteroidal antiinflammatory drugs (NSAIDs) on microbial community was analyzed. The results indicated that (1) the average diclofenac and clofibric acid removal efficiency in the 3DE-BAF firstly increased, attained the peak of 79.40 ± 6.74% and 69.50 ± 6.26% at 0.35 A, and then decreased to 71.82 ± 4.90% and 55.92 ± 5.17% at 0.40 A, respectively; (2) the concentration of the diclofenac and clofibric acid in 3DE-BAF gradually decreased with the increase of reactor height; (3) the current intensity and space position affected the microbial structure at the different level; (4) at the optimum current intensity, Thiothrix, Flavobacteriaceae, Halothiobacillaceae, Hydrogenophaga, and Comamonadaceae accounted for the main bacterial community for removal diclofenac and clofibric acid in the 3DE-BAF.

Characterization and Dynamic Shift of Microbial Communities during Start-Up, Overloading and Steady-State in an Anaerobic Membrane Bioreactor.

A lab-scale anaerobic membrane bioreactor (AnMBR) with a side stream tubular membrane was developed to treat synthetic domestic sewage to evaluate its performance and the dynamic shift of bacterial and archaeal communities during the start-up, steady-state, overloading and recovery periods of operation at mesophilic temperatures. During the start-up period, the bacterial and archaeal communities changed drastically, and Proteobacteria and Bacteroidetes predominated. During the steady-state period, the AnMBR exhibited excellent COD removal above 91%, and COD of the effluent was below 50 mg/L. High-throughput sequencing analysis results revealed that bacterial and archaeal communities shifted significantly from the start-up to the steady-state period, and that the Proteobacteria phylum predominated on days 140, 162 and 190, and the archaea community hydrogenotrophic methanogen genus Methanolinea (1.5–6.64%) predominated over the aceticlastic methanogen genus Methanothrix (1.35–3.07%). During the overloading period, significant changes occurred in microbial community on day 210, e.g., the phyla Bacteroidetes (30%), Proteobacteria (23%) and Firmicutes (18%) predominated and the archaeal community was completely suppressed, and Methanobrevibacter (0.7%) was the only methanogen genus that emerged in the overloading period. After a shock loading period, the microbial communities exhibited significant changes within the ranks of methanogens and shifted to dominance of the aceticlastic methanogen pathway. In addition, the TVFAs to alkalinity ratio in this study was suitable as an indicator of monitoring performance in the AnMBR operation.

The mechanism of enhanced wastewater nitrogen removal by photo-sequencing batch reactors based on comprehensive analysis of system dynamics within a cycle

To understand the mechanism of enhanced nitrogen removal by photo-sequencing batch reactors (photo-SBRs), which incorporated microalgal photosynthetic oxygenation into the aerobic phases of a conventional cycle, this study performed comprehensive analysis of one-cycle dynamics. Under a low aeration intensity (about 0.02 vvm), a photo-SBR, illuminated with light at 92.27 μ·mol·m−2·s−1, could remove 99.45% COD, 99.93% NH4+-N, 90.39% TN, and 95.17% TP, while the control SBR could only remove 98.36% COD, 83.51% NH4+-N, 78.96% TN, and 97.75% TP, for a synthetic domestic sewage. The specific oxygen production rate (SOPR) of microalgae in the photo-SBR could reach 6.63 fmol O2·cell−1·h−1. One-cycle dynamics shows that the enhanced nitrogen removal by photo-SBRs is related to photosynthetic oxygenation, resulting in strengthened nitrification, instead of direct nutrient uptake by microalgae. A too high light or aeration intensity could deteriorate anoxic conditions and thus adversely affect the removal of TN and TP in photo-SBRs.

Effects of influent C/N ratios and treatment technologies on integral biogas upgrading and pollutants removal from synthetic domestic sewage

Three different treatment technologies, namely mono-algae culture, algal-bacterial culture, and algal-fungal culture, were applied to remove pollutants form synthetic domestic sewage and to remove CO2 from biogas in a photobioreactor. The effects of different initial influent C/N ratios on microalgal growth rates and pollutants removal efficiencies by the three microalgal cultures were investigated. The best biogas upgrading and synthetic domestic sewage pollutants removal effect was achieved in the algal-fungal system at the influent C/N ratio of 5:1. At the influent C/N ratio of 5:1, the algal-fungal system achieved the highest mean chemical oxygen demand (COD) removal efficiency of 81.92% and total phosphorus (TP) removal efficiency of 81.52%, respectively, while the algal-bacterial system demonstrated the highest mean total nitrogen (TN) removal efficiency of 82.28%. The average CH4 concentration in upgraded biogas and the removal efficiencies of COD, TN, and TP were 93.25 ± 3.84% (v/v), 80.23 ± 3.92%, 75.85 ± 6.61%, and 78.41 ± 3.98%, respectively. These results will provide a reference for wastewater purification ad biogas upgrading with microalgae based technology.

AN INNOVATIVE CONTINUOUS FLOW BNR-IC PROCESS FOR NUTRIENTS REMOVAL AND PHOSPHORUS RECOVERY FROM SYNTHETIC AND REAL DOMESTIC WASTEWATER

An innovative continuous flow process linking biological nutrients removal (BNR) with induced crystallization (IC) was used to remove nutrients and recover phosphorus (P) from synthetic and real domestic wastewater. The results showed that a good nutrients removal performance was found regardless of feeding solutions. P recovery efficiency from synthetic wastewater was 70.2% slightly less than that from real domestic sewage (74.2%). Importantly, P recovery can effectively enhance the subsequent biological P removal. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis displayed an obvious shift in microbial community structure when switching feeding synthetic solution to real wastewater. A total of 13 bands were detected in sludge samples using synthetic and real domestic sewage, affiliated with 8 phyla or classes domain Bacteria (Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Flavobacteria, Actinobacteria, Sphingobacteria, Epsilonproteobacteria and Chlorobia). The results obtained here suggest that the continuous flow BNR-IC process is feasible for nutrients removal and P recovery from domestic sewage and is a promising technology for wastewater treatment combined with recycling of P elements.

Optimized hydraulic retention time for phosphorus and COD removal from synthetic domestic sewage with granules in a continuous-flow reactor

In continuous-flow reactor (CFR), suboptimal hydraulic retention time (HRT) can affect the substrate loading, anaerobic time and aerobic time and further affect the performance and characteristics of granules, thus different HRTs (7.5, 6.0, 4.5 and 5.2h) were tested to improve the phosphorus (P) and carbon (COD) removal of the continuous-flow system with granules in this study. When HRT was below 6.0h, the COD removal efficiency in anaerobic zone and the P removal efficiency in aerobic zone reduced obviously, and the settling ability of EBPR granules deteriorated. The residual COD in anaerobic zone resulted in the proliferation of filamentous bacteria on the granules surface. Pyrosequencing analysis revealed that Proteobacteria was the dominant phylum in this system. The dominant class transformed from Betaproteobacteria to Gammaproteobacteria when HRT was reduced from 6.0h to 4.5h.

Influence of intermittent aeration and organic loading rate on lab-scale constructed wetland systems treating synthetic wastewater

By coupling the intermittent characteristics of rural sewage discharge and solar energy density, the performance responses of lab-scale tidal flow constructed wetland (TF) and conventional vertical flow constructed wetland (VF) to different organic loading rates (OLRs) (166.3, 300.9, 451.2, 602.4, and 751.2 g/m2 d) in synthetic domestic sewage treatment were investigated to study its feasibility to replace conventional aeration and reduce the dependence of wastewater treatment plants on the grid in this study. Artificial aeration was conducted based on simulating photovoltaic aeration. The increase in OLR promoted the removal performances for the chemical oxygen demand (COD) and ammonia–nitrogen (NH4+-N) in TF, which could be up to 95.7 and 97.2%, respectively, under OLR of 751.2 g/m2 d. Excess organic carbons inhibited NH4+-N removal through competition for oxygen available in VF, where the COD removal efficiency could be 89.6% while low NH4+-N removal (40%) was obtained under OLR 751.2 g/m2 d. With the increase in OLR, the removal of total nitrogen (TN) was enhanced. A higher OLR can not only provide enough electron donors but also produce more anoxic regions for denitrification. The best TN removal was 77.5% in TF and 49.8% in VF, which occurred at OLR of 751.2 and 602.4 g/m2 d, respectively. A drop of TN removal in VF was attributed to the lack of nitrate–nitrogen (NO3--N) when reaching OLR of 751.2 g/m2 d. The removal efficiency for total phosphorus was increased gradually with the increase in OLR. This paper suggests that appropriate control of OLR can achieve the optimal effect of pollutants removal, especially the elimination of TN.

Effect of earthworm loads on organic matter and nutrient removal efficiencies in synthetic domestic wastewater, and on bacterial community structure and diversity in vermifiltration

In this paper, we studied the effect of earthworm loads on the removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total nitrogen, and total phosphorus from synthetic domestic sewage and on the bacterial community structure and diversity of substrates in earthworm packing beds. The different vermifiltrations (VFs), including the control, are successful in removing both organic matter (OM) and nutrients. The removal rate of NH3-N at 12.5 g of earthworm/L of soil VF is higher compared with that at 0 and 4.5 earthworm load VFs. The highest Shannon index, in the earthworm packing bed, occurred at 16.5 earthworm load VF. Furthermore, the COD removal rate is significantly correlated with the Shannon index, which reveals that OM removal for synthetic domestic sewage treatment at VF might be more dependent on bacterial diversity at the earthworm packing bed. The band distributions and diversities of the bacterial community for samples from different earthworm loads in VFs suggest that the bacterial community structure was only affected within the earthworm packing bed when the earthworm load reached a certain level. The present study adds to the current understanding of OM and nutrient degradation processes in VF domestic wastewater treatment.

Sulfide-Oxidizing Autotrophic Denitrification: an Evaluation for Nitrogen Removal from Anaerobically Pretreated Domestic Sewage

Nitrogen removal from effluents of anaerobic reactors using conventional nitrification/denitrification processes depends on the availability of electron donors for denitrification. As sulfide is normally present in such effluents, autotrophic denitrification using sulfide can be an alternative to avoid or reduce the requirements of exogenous organic carbon sources. This study evaluated the application of sulfide-oxidizing autotrophic denitrification to anaerobically pretreated domestic sewage. A denitrifying reactor was fed with a mixture, at different proportions, of anaerobically pretreated (containing sulfides and residual organic matter) and nitrified (containing nitrates) effluents produced by reactors treating synthetic domestic sewage. Autotrophic denitrification was responsible for most of the nitrogen removal and coexisted with heterotrophic activity, resulting in high denitrification efficiencies. Efficient denitrification could be attained at a molar NO3 (-)/S(2-) ratio of 2.1, higher than values reported before, and this represents an important parameter for the strategic application of the process. Under the experimental conditions studied, autotrophic denitrification showed to be an efficient and feasible alternative to conventional denitrification using exogenous electron donors.

Multiple factors influencing anaerobic acidogenic pretreatment in an up-flow non-woven biofilm reactor

Anaerobic acidogenesis in an up-flow non-woven biofilm reactor was investigated to convert chemical oxygen demand (COD) into volatile fatty acids (VFAs) as carbon source in the subsequent nitrogen removal process in synthetic domestic sewage pretreatment. A specifically designed non-woven padding inserted vertically into the reactor proved very favorable for acidogenic bacterial attachment. The characterization of the microorganisms was performed using scanning electron microscopy and fluorescent in situ hybridization. Multiple factors, including hydraulic retention time (HRT), pH, and influent COD and NH4+–N concentrations, played comprehensive roles in acidogenesis. Based on the Taguchi orthogonal array, the ordering sequence of the influential factors for VFAs production was influent NH4+–N (R=41.4)>pH (R=37.3)>influent COD (R=20.2)>HRT (R=14.8). The suitable conditions were HRT=1.5h, pH=8.5, influent COD=100mgL−1, and influent NH4+–N=30mgL-1. Moreover, acetic acid, propionic acid, and n-butyric acid prevailed over other VFAs. Finally, the most influential factor for each VFA was demonstrated.

Effects of various LED light wavelengths and intensities on the performance of purifying synthetic domestic sewage by microalgae at different influent C/N ratios

In Chinese rural areas, domestic sewage is one of the main sources of water pollution that may cause water eutrophication if directly discharged into natural waters without appropriate treatment. This study demonstrates that the microalgae Chlorella vulgaris can effectively remove nutrients from domestic sewage. In this process, red is the optimal light wavelength, with an intensity strategy as follows: Phase 1, 0–48h with 1000μmolm−2s−1; Phase 2, 48–96h with 1500μmolm−2s−1; Phase 3, 96–120h with 2000μmolm−2s−1; and Phase 4, 120–144h with 2500μmolm−2s−1. The optimal cultivation time was 144h. Nutrient removal efficiency was significantly affected by the light wavelength, light intensity, the effect of the interaction between light wavelength and intensity, as well as the effect of the interaction among light wavelength, light intensity, and influent C/N ratio. Moreover, the total nitrogen and total phosphorus removal efficiencies were significantly affected by the influent C/N ratio. In this study, the optimal influent C/N ratio is 5:1.

Effect of C/N ratios on the performance of earthworm eco-filter for treatment of synthetics domestic sewage

The performances of filter systems that use earthworms and plants, combined with earthworm eco-filter (EE) systems in treating synthetic domestic sewage (SDS) with different C/N ratios, were investigated for a 9-month period. The effects of the combination of filters, earthworms, plants, as well as the combination of earthworms and plants on SDS nutrient removal efficiency were separately investigated to select the optimum system for treating SDS. The results of the current study could be used to determine how treatment performance responds to different C/N ratios and to explain and predict the performance of an operating EE system. EE systems with earthworms and plants (EP groups) consistently performed better than the other types of systems (CK, E, and P; that is, without earthworms and without plants, with earthworms and without plants, and without earthworms and with plants, respectively) under all C/N ratios. The highest removal efficiencies of chemical oxygen demand, total nitrogen, total phosphorus, and total organic carbon were achieved under C/N ratios of 6:1, 6:1, 6:1, and 9:1, respectively. The optimum nutrient removal efficiency was achieved at C/N = 6, and the contribution order for nutrient removal was EP > P > E > CK. Influent C/N ratios, the time of year, and the synergetic effects of earthworm behavior and microorganisms significantly affected nutrient removal efficiencies. Considering the removal of all nutrients, EE systems with plants and earthworms achieved optimum removal effects in July when the influent C/N ratio was controlled at 6. Appropriate control of carbon and nitrogen source concentrations permitted the achievement of optimal nutrient removal effects.

Treatment of domestic sewage by a metal membrane bioreactor

A submerged flat metal MBR (membrane bioreactor) was used to treat synthetic domestic sewage in this study. The experiment was continued for 270 days and ran under two modes as AMBR (aerobic membrane bioreactor) and A/O-MBR (anoxic/aerobic membrane bioreactor) at a permeate flux of 0.4-1 m³/(m² d). PVA (polyvinyl alcohol) gel beads were added to the aeration tank with a volume ratio of 10% at the end of the A/O-MBR mode. The mean COD and TN removal efficiencies achieved 96.69 and 32.12% under the AMBR mode, and those were 92.17 and 72.44% under the A/O-MBR mode, respectively. SND (simultaneous nitrification and denitrification) occurred at high MLSS (mixed liquor suspended solids) concentration. The metal membranes reduced effluent COD during filtration. The system ran stably for 115 days at a permeate flux of 0.8-1 m³/(m² d) without changing membranes under the AMBR mode, but the membrane filterability decreased gradually under high MLSS or A/O-MBR mode, and the addition of PVA worsened the membrane filterability on the contrary. PSD (particle size distribution) and sludge fractions had evident influence on membrane fouling. The main fouling mechanism was cake formation under the AMBR mode, and that was pore blocking under the A/O-MBR mode.

Determination of the intrinsic kinetic parameters of sulfide-oxidizing autotrophic denitrification in differential reactors containing immobilized biomass

Nitrogen removal coupled with sulfide oxidation has potential for the treatment of effluents from anaerobic reactors because they contain sulfide, which can be used as an endogenous electron donor for denitrification. This work evaluated the intrinsic kinetics of sulfide-oxidizing autotrophic denitrification via nitrate and nitrite in systems containing attached cells. Differential reactors were fed with nitrified synthetic domestic sewage and different sulfide concentrations. The intrinsic kinetic parameters of nitrogen removal were determined when the mass transfer resistance was negligible. This bioprocess could be described by a half-order kinetic model for biofilms. The half-order kinetic coefficients ranged from 0.425 to 0.658mgN1/2L−1/2h−1 for denitrification via nitrite and from 0.190 to 0.609mgN1/2L−1/2h−1 for denitrification via nitrate. In this latter, the lower value was due to the use of electrons donated from intermediary sulfur compounds whose formation and subsequent consumption were detected.

Kinetic evaluation of the psychrophylic anaerobic digestion of synthetic domestic sewage using an upflow filter

A study of the anaerobic digestion process of synthetic domestic sewage (total COD: 705 mg/L) was carried out. The digestion was conducted in an upflow anaerobic filter with corrugated plastic rings as packing media at psychrophilic temperature (15–17 °C). For HRTs of between 10.0 and 17.1 h, the total COD removal efficiency was almost constant and independent on the HRT, achieving an average value of around 80%. However, when the HRT decreased from 7.0 to 3.2 h the efficiency diminished from 77% to 65%. This decrease in removal efficiency was parallel to the increase in the VFA/Alkalinity ratio for this HRT range. The flow pattern observed in the reactor studied was intermediate between plug-flow and CSTR systems, although the plug-flow was predominant. It can also be observed that Young and McCarty’s model almost coincided with the CSTR model, when the biodegradable COD was used for fitting the data. The Manariotis equation allowed a better fit of the experimental data (total COD removal efficiency with influent substrate concentration and HRT) than the Young model. The methane yield coefficient obtained was 0.15 L CH 4/g COD consumed.

Experimental study of domestic sewage treatment with a metal membrane bioreactor

A novel stainless steel membrane module with a 0.2 μm nominal pore diameter was applied in an aerated submerged membrane bioreactor to treat synthetic domestic sewage. The pore size of metal membrane was more homogeneous and of tighter distribution than that of organic membrane. The steady membrane flux was more than 17 Lm −2h −1. The mean COD removal efficiency achieved 97.0%. The mean NO − 3-N/TN ratio was 74.6% in effluent. There was a certain positive correlation between membrane fouling and extraceller polymeric substances of activated sludge solution. Membrane fouling could be effectively alleviated by the on-line backwash and intermittent running mode. In addition, membrane fouling could be eliminated almost entirely by off-line cleaning with 0.25% (wt) NaClO solution with pH 12. After off-line cleaning, membrane flux could be recovered by about 93.3%. These results implied that it was economical for using the stainless steel membrane in a membrane bioreactor for wastewater treatment.

Simultaneous carbon and nitrogen removal in a mixed culture aerobic RBC biofilm

A mixed culture biofilm was developed with a sulfur oxidising, heterotrophic bacterium Thiosphaera pantotropha, autotrophic nitrifiers and other heterotrophs in a three stage rotating biological contactor (RBC). Specific benefits due to peculiar properties of T. pantotropha of simultaneous heterotrophic nitrification and aerobic denitrification were derived in the reactor investigated for a combined carbon and nitrogen removal from a synthetic domestic sewage. The first stage biofilm which contained T. pantotropha showed high COD and NH 4 +-N removal rates of 5.8–14.1 g COD/m 3·d and 0.47–1.1 g N/m 2·d for the corresponding loading rates of 6.9–20.7 g COD/m 3·d and 0.69–2.09 g N/m 2·d, respectively. Contrary to the conventional units designed for a concurrent carbon removal and nitrification, the nitrification rates increased linearly with an increase in organic loading rate before stabilising at about 1 g N/m 2·d corresponding to a COD loading rate of about 15 g/m 2·d and a nitrogen loading rate of 1.5 g N/m 2·d showing a change in the order of reaction from first to zero. A simultaneous nitrogen removal of 20–68% was also obtained. The system's performance indicated that a single stage aerobic biofilm can be developed to meet the increasingly stringent regulations on effluent nitrogen discharges affording several advantages over the conventional systems, e.g. low buffer requirements, no need for external carbon source for denitrification, etc., which may result in substantial reduction in the treatment cost.