Anaerobic ammonium oxidation for advanced municipal wastewater treatment: is it feasible?

Anaerobic ammonium oxidation（ANAMMOX） is a recently developed process to treat ammonia-rich wastewater. There were numerous articles about the new technology with focus on the ammonium-rich wastewater treatment, but few on advanced municipal wastewater treatment. The paper studied the anaerobic ammonium oxidation （ANAMMOX） process with a down flow anoxic biofilter for nitrogen removal from secondary clarifier effluent of municipal wastewater with low COD/N ratio. The results showed that ANAMMOX process is applicable to advanced wastewater treatment with normal temperature as well as ammonia-rich high temperature wastewater treatment. The results indicated that ammonia removal rate was improved by raising the nitrite concentration, and the reaction rate reached a climax at 118.4 mgN/L of the nitrite nitrogen concentration. If the concentration exceeds 118.4 mgN/L, the ANAMMOX process was significantly inhibited although the ANAMMOX bacteria still showed a relatively high reactivity. The data also indicated that the ratio of NO2^- -N：NH4 ＊ -N = 1.3：1 in the influent was appropriate for excellent nitrogen removal. The pH increased gradually along the ANAMMOX biofilter reactor. When the ANAMMOX reaction was ended, the pH was tend to calm. The data suggested that the pH could be used as an indicator to describe the course of ANAMMOX reaction.     

Nitrogen and phosphorus removal in an airlift intermittent circulation membrane bioreactor

A new airlift intermittent circulation integrated bioreactor was developed for simultaneous nitrogen and phosphorus removal of wastewater, in which, circulation of mixed liquid between mixing zone and aeration zone was realized by aeration power, alternately anaerobic/anoxic bio-environment in mixing zone was realized by intermittent circulation and simultaneous nitrogen and phosphorus removal was obtained through strengthened denitrifying phosphorus removal process. Removal performance of the reactor was investigated and pollutant removal and transfer mechanism in one operation circle was analyzed. The experiment results indicated that under the influent condition of chemical oxygen demand (COD) concentration of 642.1 mg/L, total nitrogen (TN) of 87.4 mg/L and PO₄^3--P of 12.1 mg/L, average removal efficiencies of COD, TN and PO₄^3--P reached 96.4%, 83.2% and 90.5%, respectively, with the hydraulic residence time of 22 hr and operation circle time of 185 min. Track studies indicated that the separation of aeration and mixing zones and intermittent circulation of mixed liquid between the two zones provided distinct biological environments spatially and temporally, which ensured the occurrence of multifunctional microbial reactions.     

Removal of nitrogen and phosphorus in a combined A2/O-BAF system with a short aerobic SRT

A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter （A^2/O-BAF） combined system was carded out to treat wastewater with lower C/N and C/P ratios. The A^2/O process was operated in a short aerobic sludge retention time （SRT） for organic pollutants and phosphorus removal, and denitrification. The subsequent BAF process was mainly used for nitrification. The BAF effluent was partially returned to anoxic zone of the A^2/O process to provide electron acceptors for denitrification and anoxic P uptake. This unique system formed an environment for reproducing the denitdfying phosphate-accumulating organisms （DPAOs）. The ratio of DPAOs to phosphorus accumulating organisms （PAOs） could be maintained at 28% by optimizing the organic loads in the anaerobic zone and the nitrate loads into the anoxic zone in the A^2/O process. The aerobic phosphorus over-uptake and discharge of excess activated sludge was the main mechanism of phosphorus removal in the combined system. The aerobic SRT of the A^2/O process should meet the demands for the development of aerobic PAOs and the restraint on the nitrifiers growth, and the contact time in the aerobic zone of the A^2/O process should be longer than 30 min, which ensured efficient phosphorus removal in the combined system. The adequate BAF effluent return rates should be controlled with 1--4 mg/L nitrate nitrogen in the anoxic zone effluent of A^2/O process to achieve the optimal nitrogen and phosphorus removal efficiencies.     

Nitrogen removal from coal gasification wastewater by activated carbon technologies combined with short-cut nitrogen removal process

A system combining granular activated carbon and powdered activated carbon technologies along with shortcut biological nitrogen removal （GAC-PACT-SBNR） was developed to enhance total nitrogen （TN） removal for anaerobically treated coal gasification wastewater with less need for external carbon resources. The TN removal efficiency in SBNR was significantly improved by introducing the effluent from the GAC process into SBNR during the anoxic stage, with removal percentage increasing from 43.8%49.6% to 68.8%-75.8%. However, the TN removal rate decreased with the progressive deterioration of GAC adsorption. After adding activated sludge to the GAG compartment, the granular carbon had a longer service-life and the demand for external carbon resources became lower. Eventually, the TN removal rate in SBNR was almost constant at approx. 43.3%, as compared to approx. 20.0% before seeding with sludge. In addition, the production of some alkalinity during the denitrification resulted in a net savings in alkalinity requirements for the nitrification reaction and refractory chemical oxygen demand （COD） degradation by autotrophic bacteria in SBNR under oxic conditions. PACT showed excellent resilience to increasing organic loadings. The microbial community analysis revealed that the PACT had a greater variety of bacterial taxons and the dominant species associated with the three compartments were in good agreement with the removal of typical pollutants. The study demonstrated that pre-adsorption by the GAC-sludge process could be a technically and economically feasible method to enhance TN removal in coal gasification wastewater （CGW）.     

Removal of nitrogen from wastewater with perennial ryegrass/artificial aquatic mats biofilm combined system

To develop a cost-effective combined phytoremediation and biological process,a combined perennial ryegrass/artificial aquatic mat biofilm reactor was used to treat synthetic wastewater.Influent ammonium loading,reflux ratio,hydraulic retention time(HRT) and temperature all had significant effects on the treatment efficiency.The results indicated that the effluent concentration of ammonium increased with increasing influent ammonium loading.The reactor temperature played an important role in the nitrification process.The ammonium removal efficiency significantly decreased from 80% to 30%-50% when the reactor temperature dropped to below 10°C.In addition,the optimal nitrogen removal condition was a reflux ratio of 2.The nitrate and ammonium concentration of the effluent were consistent with the HRT of the combined system.The chemical oxygen demand(COD) removal efficiency was at a high level during the whole experiment,being almost 80% after the start-up,and then mostly above 90%.The direct uptake of N by the perennial ryegrass accounted for 18.17% of the total N removal by the whole system.The perennial ryegrass absorption was a significant contributor to nitrogen removal in the combined system.The result illustrated that the combined perennial ryegrass/artificial aquatic mat biofilm reactor demonstrated good performance in ammonium,total N and COD removal.     

Biological removal of antiandrogenic activity in gray wastewater and coking wastewater by membrane reactor process

A recombinant human androgen receptor yeast assay was applied to investigate the occurrence of antiandrogens as well as the mechanism for their removal during gray wastewater and coking wastewater treatment. The membrane reactor (MBR) system for gray wastewater treatment could remove 88.0% of antiandrogenic activity exerted by weakly polar extracts and 97.3% of that by moderately strong polar extracts, but only 32.5% of that contributed by strong polar extracts. Biodegradation by microorganisms in the MBR contributed to 95.9% of the total removal. After the treatment, the concentration of antiandrogenic activity in the effluent was still 1.05 μg flutamide equivalence (FEQ)/L, 36.2% of which was due to strong polar extracts. In the anaerobic reactor, anoxic reactor, and membrane reactor system for coking wastewater treatment, the antiandrogenic activity of raw coking wastewater was 78.6 mg FEQ/L, and the effluent of the treatment system had only 0.34 mg FEQ/L. The antiandrogenic activity mainly existed in the medium strong polar and strong polar extracts. Biodegradation by microorganisms contributed to at least 89.2% of the total antiandrogenic activity removal in the system. Biodegradation was the main removal mechanism of antiandrogenic activity in both the wastewater treatment systems.     

The plant-enhanced bio-cathode: Root exudates and microbial community for nitrogen removal

A plant bio-electrochemical system(PBES) was constructed for organic pollutant removal and power generation. The bio-cathode, composed of granular activated carbon(GAC), stainless wire mesh and a plant species(Triticum aestivum L.), was able to catalyze cathodic reactions without any requirement for aeration or power input. During the 60-day-long operation, an average voltage of 516 m V(1000 Ω) and maximum power density(Pmax) of 0.83 W/m~3 were obtained in the PBES. The total nitrogen removal and total organic carbon removal in the PBES were 85% and 97%, respectively. Microbial community analyses indicated that bacteria associated with power generation and organic removal were the predominant species in the bio-cathode, and plant-growth-promoting rhizobacteria were also found in the PBES. The results suggested that the coupling of plants with the GAC cathode may enhance the organicmatter degradation and energy generation from wastewater and therefore provide a new method for bio-cathode design and promote energy efficiency.     

Elucidating the removal mechanism of N,N-dimethyldithiocarbamate in an anaerobic-anoxic-oxic activated sludge system

N,N-Dimethyldithiocarbamate （DMDTC） is a typical precursor of N-nitrosodimethylamine （NDMA）. Based on separate hydrolysis, sorption and biodegradation studies of DMDTC, a laboratory-scale anaerobic-anoxic-oxic （AAO） system was established to investigate the removal mechanism of DMDTC in this nutrient removal biological treatment system. DMDTC hydrolyzed easily in water solution under either acidic conditions or strong alkaline conditions, and dimethylamine （DMA） was the main hydrolysate. Under anaerobic, anoxic or oxic conditions, DMDTC was biodegraded and completely mineralized. Furthermore, DMA was the main intermediate in DMDTC biodegradation. In the AAO system, the optimal conditions for both nutrient and DMDTC removal were hydraulic retention time 8 hr, sludge retention time 20 day, mixed-liquor return ratio 3：1 and sludge return ratio 1：1. Under these conditions, the removal efficiency of DMDTC reached 99.5%; the removal efficiencies of chemical organic demand, ammonium nitrogen, total nitrogen and total phosphorus were 90%, 98%, 81% and 93%, respectively. Biodegradation is the dominant mechanism for DMDTC removal in the AAO system, which was elucidated as consisting of two steps： first, DMDTC is transformed to DMA in the anaerobic and anoxic units, and then DMA is mineralized to CO2 and NH3 in the anoxic and oxic units. The mineralization of DMDTC in the biological treatment system can effectively avoid the formation of NDMA during subsequent disinfection processes.     

Simultaneous phosphorus and nitrogen removal in a continuous-flow two-sludge system

The ability of simultaneous biological phosphorus and nitrogen removal was investigated in a lab-scale continuous-flow two-sludge system. Alternating anaerobic and anoxic conditions were combined with contact oxidation stage for treating raw municipal wastewater. Long-term experiments showed that the contradiction of competing for the organic substrate between denitrifying bacteria and PAOs （phosphorus accumulating organisms） in traditional phosphorus and nitrogen removal system has been resolved. The system can adapt to low influent COD/TN ratio （C/N）. Furthermore the SRT （sludge retention time） of nitrifying sludge and denitrifying phosphorus removal sludge can be controlled at optimal conditions respectively. The removal efficiency of COD, TP, TN, and NH4-N was 81.78%, 92.51%, 75.75%, and 84.47% respectively. It was also found that the appropriate influent C/N should be controlled at the range of 3.8-6, while the optimal C/N to the system ranged between 4-5, and the BFR （bypass sludge flow rate） should be controlled at 0.35 around.     

Evaluation of a cost e ective technique for treating aquaculture water discharge using Lolium perenne Lam as a biofilter

Wastewater stabilization ponds generate low cost by-products that are useful for agriculture. The utilization of these by-products for soil amendment and as a source of nutrients for plants requires a high level of sanitation and stabilization of the organic matter, to maintain acceptable levels of soil, water and air quality. In this study, two aquaculture wastewater treatment systems; recirculating system and a floating plant bed system were designed to improve the quality of irrigation water in local communities with low income. In both systems the grass species Lolium perenne Lam was used as a plant biofilter while vegetable specie Amaranthus viridis was used to evaluate the performance of the system and the suitability of the phyto-treated water for irrigation. It was found that the harmful material removal rate for recirculating system was 88.9% for TAN （total ammonia nitrogen）, 90% for NO2--N, 64.8% for NO3--N while for floating plant bed system 82.7% for TAN, 82% for NO2--N and 60.5% for NO3--N. Comparative analysis of the efficiency of waste element removal between the two systems revealed that both systems performed well, however, plant growth was not robust for floating plant bed system while recirculating system is energy consuming. Although both systems did not attain sufficient levels of TN （total nitrogen） and TP （total phosphorus） load reduction, the treatment with L. perenne remarkably improved the irrigation water quality. A. viridis plants irrigated with the phyto-treated discharge water had lesser concentrations of heavy metals in their tissues compared to those irrigated with untreated discharge. The control plants irrigated with untreated discharge were also found to be highly lignified with few stems and small leaves.     

Microalgae cultivation using an aquaculture wastewater as growth medium for biomass and biofuel production

Microalgae as a main feedstock has attracted much attention in recent years but is still not economically feasible due to high algal culture cost. The objective of this study was to develop a comprehensive eco-friendly technology for cultivating microalgae Platymonas subcordiformis using aquaculture wastewater as growth medium for biomass and biofuel production. Platymonas subcordiformis was grown in pretreated flounder aquaculture wastewaters taken from different stages. Each of wastewater contained different levels of nutrients. The biomass yield of microalgae and associated nitrogen and phosphorous removal were investigated. The results showed that algal cell density increased 8.9 times than the initial level. Platymonas subcordiformis removed nitrogen and phosphorus from wastewater with an average removal efficiency of 87%-95% for nitrogen and 98%-99% for phosphorus. It was feasible to couple the removal of nitrogen and phosphorus from wastewater to algal biomass and biofuel production. However, further studies are required to make this technologies economically viable for algae biofuel production.     

Contaminant removal from low-concentration polluted river water by the bio-rack wetlands

The bio-rack is a new approach for treating low-concentration polluted river water in wetland systems. A comparative study of the efficiency of contaminant removal between four plant species in bio-rack wetlands and between a bio-rack system and control system was conducted on a small-scale (500 mm length × 400 mm width × 400 mm height) to evaluate the decontamination effects of four different wetland plants. There was generally a significant difference in the removal of total nitrogen (TN), ammonia nitrogen (NH₃-N) and total phosphorus (TP), but no significant difference in the removal of permanganate index (COD_Mn) between the bio-rack wetland and control system. Bio-rack wetland planted with Thalia dealbata had higher nutrient removal rates than wetlands planted with other species. Plant fine-root (root diameter ≤ 3 mm) biomass rather than total plant biomass was related to nutrient removal efficiency. The study suggested that the nutrient removal rates are influenced by plant species, and high fine-root biomass is an important factor in selecting highly effective wetland plants for a bio-rack system. According to the mass balance, the TN and TP removal were in the range of 61.03--73.27 g/m² and 4.14--5.20 g/m² in four bio-rack wetlands during the whole operational period. The N and P removal by plant uptake constituted 34.9%--43.81% of the mass N removal and 62.05%--74.81% of the mass P removal. The study showed that the nitrification/denitrification process and plant uptake process are major removal pathways for TN, while plant uptake is an effective removal pathway for TP.     

Performance and microbial community of a membrane bioreactor system——Treating wastewater from ethanol fermentation of food waste

In this study, a lab-scale biological anaerobic/anaerobic/anoxic/membrane bioreactor(A_-~3MBR) was designed to treat wastewater from the ethanol fermentation of food waste,a promising way for the disposal of food waste and reclamation of resources. The 454 pyrosequencing technique was used to investigate the composition of the microbial community in the treatment system. The system yielded a stable effluent concentration of chemical oxygen demand(202 ± 23 mg/L), total nitrogen(62.1 ± 7.1 mg/L), ammonia(0.3 ±0.13 mg/L) and total phosphorus(8.3 ± 0.9 mg/L), and the reactors played different roles in specific pollutant removal. The exploration of the microbial community in the system revealed that:(1) the microbial diversity of anaerobic reactors A_1 and A_2, in which organic pollutants were massively degraded, was much higher than that in anoxic A_3 and aerobic MBR;(2) although the community composition in each reactor was quite different, bacteria assigned to the classes Clostridia, Bacteroidia, and Synergistia were important and common microorganisms for organic pollutant degradation in the anaerobic units, and bacteria from Alphaproteobacteria and Betaproteobacteria were the dominant microbial population in A_3 and MBR;(3) the taxon identification indicated that Arcobacter in the anaerobic reactors and Thauera in the anoxic reactor were two representative genera in the biological process. Our results proved that the biological A_-~3MBR process is an alternative technique for treating wastewater from food waste.     

Nitrogen removal influence factors in A/O process and decision trees for nitrification/denitrification system

In order to improve nitrogen removal in anoxic/oxic(NO) process effectively for treating domestic wastewaters, the influence factors, DO( dissolved oxygen), nitrate recirculation, sludge recycle, SRT( solids residence time), influent COD/TN and HRT( hydraulic retention time) were studied. Results indicated that it was possible to increase nitrogen removal by using corresponding control strategies,such as, adjusting the DO set point according “to effluent ammonia concentration; manipulating nitrate recirculation flow according to nitrate concentration at the end of anoxic zone. Based on the experiments results, a knowledge-based approach for supervision of the nitrogen removal problems was considered, and decision trees for diagnosing nitrification and denitrification problems were built and successfully applied to NO process.     

Effects of seawater salinity on nitrite accumulation in short-range nitrification to nitrite as end product

The effect of seawater salinity on nitrite accumulation in short-range nitrification to nitrite as the end product was studied by using a SBR. Experimental results indicated that the growth of nitrobacteria was inhibited and very high levels of nitrite accumulation at different salinities were achieved under the conditions of 25--28℃, pH 7.5--8.0, and the influent ammonia nitrogen of 40--70mg/L when seawater flow used to flush toilet was less than 35% (salinity 12393 mg/L, Cl^- 6778mg/L) of total domestic wastewater flow, which is mainly ascribed to much high chlorine concentration of seawater. Results showed that high seawater salinity is available for short-range nitrification to nitrite as the end product. When the seawater flow used to flush toilet accounting for above 70% of the total domestic wastewater flow, the removal efficiency of ammonia was still above 80% despite the removal of organics declined obviously(less than 60% ). It was found that the effect of seawater salinity on the removal of organics was negative rather than positive one as shown for ammonia removal.     

Treatment of coke plant wastewater by SND fixed biofilm hybrid system

In this article, coke plant wastewater was treated by a simultaneous nitrifying and denitrifying （SND） fixed biofilm hybrid system. The results showed that suitable parameters of the system were important for the performance of the bio-degradation system. The chemical oxygen demand （COD） removal efficiency in this system was satisfactory, higher than 94%, and ammonia nitrogen was higher than 95%. The effluent COD concentration could meet the discharge standard, except for very few situations. The results showed that a sufficient carbon source was important for making ammonia nitrogen concentration meet the discharge standard. Then the TiN removal efficiency in this system can be brought higher than 94%. Dissolved oxygen （DO） is very important to the performance of the SND bio-degradation system, and the suitable DO is about 3.5-4.0 mg/L at the forepart of reactor. In addition, the performance of the system was almost not affected by pH value. The results show that the system is feasible to treat coke plant wastewater.     

Algal uptake of dissolved organic nitrogen in wastewater treatment plants

The algal uptake of dissolved organic nitrogen(DON) in the anaerobic–anoxic–oxic(A_2O)process was investigated in this study. Anaerobic, aerobic and effluent DON samples from two wastewater treatment plants(WWTPs) were separated into hydrophilic and hydrophobic fractions using a DAX-8 resin coupled with an anion exchange resin and a nanofiltration(NF)pretreatment. Hydrophilic DON accounted for 66.66%–88.74% of the entire DON for the two plants evaluated. After a 15-day incubation, 16.95%–91.75% DON was bioavailable for algal growth, and untreated samples exhibited higher DON bioavailability, with 52.83% DON average uptake rates, compared with the hydrophilic and hydrophobic fractions(45.53% and 44.40%, respectively) because the pretreatment caused the inorganic salt to be resistant to algae. Anaerobic untreated samples, hydrophilic fractions and hydrophobic fractions showed higher DON reduction rates and higher biomass accumulation compared with the other DON fractions due to the decomposition of resistant organics by anaerobic and anoxic bacteria.DON in aerobic and effluent samples of plant A was more bioavailable than that of plant B with usages of 27.49%–55.26% DON. DON bioavailability in the anaerobic–anoxic–oxic process decreased in the following order: anaerobic effluent aerobic. The DON contents were reduced after anaerobic treatment in the two plants. The EEM-PARAFAC model identified three DON components, including two humic acid-like substances and one protein-like substance in plant A and two protein-like substances and one humic acid-like substance in plant B.     

Simultaneous removal of COD and nitrogen using a novel carbon-membrane aerated biofilm reactor

A membrane aerated biofilm reactor is a promising technology for wastewater treatment. In this study, a carbon-membrane aerated biofilm reactor （CMABR） has been developed, to remove carbon organics and nitrogen simultaneously from one reactor. The results showed that CMABR has a high chemical oxygen demand （COD） and nitrogen removal efficiency, as it is operated with a hydraulic retention time （HRT） of 20 h, and it also showed a perfect performance, even if the HRT was shortened to 12 h. In this period, the removal efficiencies of COD, ammonia nitrogen （NH4^＋-N）, and total nitrogen （TN） reached 86%, 94%, and 84%, respectively. However, the removal efficiencies of NH4^＋-N and TN declined rapidly as the HRT was shortened to 8 h. This is because of the excessive growth of biomass on the nonwoven fiber and very high organic loading rate. The fluorescence in situ hybridization （FISH） analysis indicated that the ammonia oxidizing bacteria （AOB） were mainly distributed in the inner layer of the biofilm. The coexistence of AOB and eubacteria in one biofilm can enhance the simultaneous removal of COD and nitrogen.     

Inhibition effect of magnetic field on nitrous oxide emission from sequencing batch reactor treating domestic wastewater at low temperature

This study aims to investigate the effect of a magnetic field on nitrous oxide(N_2O) emission from a sequencing batch reactor treating low-strength domestic wastewater at low temperature(10℃).After running for 124 days in parallel,results indicated that the conversion rate of N_2O for a magnetic field-sequencing batch reactor(MF-SBR) decreased by34.3% compared to that of a conventional SBR(C-SBR).Meanwhile,the removal efficiencies for total nitrogen(TN) and ammonia nitrogen(NH4-N) of the MF-SBR were 22.4% and 39.5% higher than those of the C-SBR.High-throughput sequencing revealed that the abundances of AOB(Nitrosomonas),NOB(Nitrospira) and denitrifiers(Zoogloea),which could reduce N_2O to N_2,were promoted significantly in the MF-SBR.Enzyme activities(Nir) and gene abundances(nos Z nir S and nir K) for denitrification in the MF-SBR were also notably higher compared to C-SBR.Our study shows that application of a magnetic field is a useful approach for inhibiting the generation of N_2O and promoting the nitrogen removal efficiency by affecting the microbial characteristics of sludge in an SBR treating domestic wastewater at low temperature.     

Graphene-supported nanoscale zero-valent iron：Removal of phosphorus from aqueous solution and mechanistic study

Excess phosphorus from non-point pollution sources is one of the key factors causing eutrophication in many lakes in China,so finding a cost-effective method to remove phosphorus from non-point pollution sources is very important for the health of the aqueous environment. Graphene was selected to support nanoscale zero-valent iron(nZVI)for phosphorus removal from synthetic rainwater runoff in this article. Compared with nZVI supported on other porous materials,graphene-supported nZVI(G-nZVI) could remove phosphorus more efficiently. The amount of nZVI in G-nZVI was an important factor in the removal of phosphorus by G-nZVI,and G-nZVI with 20 wt.% nZVI(20% G-nZVI)could remove phosphorus most efficiently. The nZVI was very stable and could disperse very well on graphene,as characterized by transmission electron microscopy(TEM) and scanning electron microscopy(SEM). X-ray photoelectron spectroscopy(XPS),Fourier Transform infrared spectroscopy(FT-IR) and Raman spectroscopy were used to elucidate the reaction process,and the results indicated that Fe-O-P was formed after phosphorus was adsorbed by G-nZVI. The results obtained from X-ray diffraction(XRD) indicated that the reaction product between nZVI supported on graphene and phosphorus was Fe3(PO4)2·8H2O(Vivianite). It was confirmed that the specific reaction mechanism for the removal of phosphorus with nZVI or G-nZVI was mainly due to chemical reaction between nZVI and phosphorus.