Efficient nitrogen removal by multi-stage A/O mud membrane composite process with segmented influent: Performance and microbial community structure

In this paper, a multi-stage A/O mud membrane composite process with segmented influent was constructed for the first time and compared with the traditional activated sludge process and the multi-stage A/O pure membrane process with segmented influent. The nitrogen removal efficiency of the process under different influencing factors was studied. Under the optimum conditions, the highest removal rate of ammonia nitrogen can reach 99%, and the average removal rate of total nitrogen was 80%. The removal rate of COD in effluent reached 93%. The relative abundance of Proteobacteria was the highest in the multi-stage A/O mud membrane composite reactor with segmented influent. The community diversity and richness of activated sludge and biofilm in aerobic pool were the highest. Dechloromonas, Flavobacterium and Rhodobacter were dominant bacteria, and they were aerobic denitrifying bacteria that significantly contributed to the removal rate of ammonia nitrogen.

Multivariate effect of inorganic wastewater matrix on the removal of pesticides by solar photo-Fenton

An amount of works has reported the effect of wastewater matrix composition on pollutants removal by different AOPs. The biggest challenge is that each wastewater source has a challenging composition (organic and inorganic compounds, pollutants, etc.) and not only the concentration of all these species but also the interaction between them may affect the effectiveness of the studied process. This work has been carried out to evaluate the photo-degradation kinetics of six different pesticides (flutriafol, imidacloprid, myclobutanil, pirimicarb, thiamethoxam and triadimenol) by solar photo-Fenton (SPF) process at acidic pH. First, oxidant concentration (H2O2) was optimized with an actual WWTP effluent. Then, the process was validated with two different secondary and tertiary WWTP effluents, in which main intermediate transformation by-products were identified. Finally, the effect of the inorganic water matrix components (bicarbonate, chloride, sulphate, nitrate and phosphate) was evaluated by a multivariate analysis. Once H2O2 has been optimized at 30 mg L-1, the photo-degradation efficiency of pesticides in real wastewater samples was compared. DOC content of both secondary and tertiary WWTP effluents was dropped by 67%. The identification of the main intermediate transformation by-products (such as 1H-1,2,4-triazole, desmethyl-formamido pirimicarb, thiamethoxam urea, chloronicotinic acid and imidacloprid urea) was reviewed. Following, the multivariate analysis on pesticides photo-degradation, generally, predicted four significant effects in common for the studied pesticides: a positive effect (interaction bicarbonate/nitrate) and three negative ones (chloride, phosphate and the interaction chloride/sulphate); among others. In addition, optimum values of inorganic ion concentrations, to obtain an optimum desirability on studied pesticides removal by SPF at acidic pH, were also evaluated.

Domestication and pilot-scale culture of mixed bacteria HY-1 capable of heterotrophic nitrification-aerobic denitrification

To further investigate the potential of heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria for practical applications, the HN-AD mixed bacteria HY-1 were enriched and domesticated in this study. After five generations of domestication, the mixture was able to remove 98% of ammonia nitrogen (400 mg/L) and 81.9% of mixed nitrogen source (nitrate, nitrite). Changes in community structure in the domestication process of mixed microorganisms were studied using 16S rDNA-seq. The results indicated an increase in the abundance of Acinetobacter from 16.9% to 80%. The conditions for the expanded culture of the HY-1 were also optimized. Moreover, A pilot-scale expanded reactor with a capacity of 1000L was constructed, and the HY-1 was successfully expanded from 0.1L to 800L. The community structures of the HY-1 remained stable after the expanded culture, with Acinetobacter as the dominant species. Moreover, the HY-1 demonstrated adaptability to actual high ammonia nitrogen wastewater and showed potential for practical application.

Cu-based perovskite as a novel CWPO catalyst for petroleum refining wastewater treatment: Performance, toxicity and mechanism

For the first time, Cu-based perovskite oxides were used as catalysts to treat highly toxic and refractory petroleum refining wastewater based on catalytic wet peroxide oxidation (CWPO) technology. Perovskite La₂CuO₄ was synthesized by sol-gel method. A series of characterizations showed that the synthesized catalyst particles are tetragonal phase perovskite structure. The experimental results showed that under the conditions of catalyst dosage of 0.75 g, temperature of 100 ℃ and reaction time of 30 min, the COD removal rate was 89.58 %, the TOC removal rate was 87.38 %. The morphology and structure of the catalyst before and after the reaction proved that the catalyst has strong stability and catalytic activity. The components of raw water, Wet Air Oxidation (WAO) effluent and CWPO effluent were compared and analyzed by Gas Chromatography-Mass Spectrometry (GC-MS), and the possible mechanism and path of WAO and CWPO degradation of petroleum refining wastewater were further explored. The changes of Cu components in La₂CuO₄ before and after CWPO reaction and the transformation of lattice oxygen and adsorbed oxygen were analyzed by X-ray Photoelectron Spectroscopy (XPS). The involvement of Cu (Ⅱ) /Cu (Ⅰ) in the activation of H₂O₂ was speculated. Finally, the biotoxicity of raw water, WAO effluent and CWPO effluent was predicted. The results provide reference value for the application of catalyst La₂CuO₄ in various petrochemical wastewater.

A review of anammox-based nitrogen removal technology: From microbial diversity to engineering applications

The anaerobic ammonium oxidation (anammox) process has the advantages of high efficiency and low energy consumption, so it has broad application prospects in biological denitrification of wastewater. However, the application of anammox technology to existing wastewater treatment is still challenging. The main problems are the insufficient supply of nitrite and the susceptibility of anammox bacteria to environmental factors. In this paper, from the perspective of the diversity of anammox bacteria, the habitats and characteristics of anammox bacteria of different genera were compared. At the same time, laboratory research and engineering applications of anammox technology in treating wastewater from different sources were reviewed, and the progress of and obstacles to the practical application of anammox technology were clarified. Finally, a focus for future research was proposed to intensively study the water quality barrier factors of anammox and its regulation strategies. Meanwhile, a combined process was developed and optimized on this basis.

Small biochar addition enhanced anammox granular sludge system for practical wastewater treatment: Performance and microbial community

Anaerobic ammonium oxidation (Anammox) granular sludge (AnGS) has poor strength and is prone to disintegration under complex environmental conditions, especially in the presence of complex organic carbon, which renders the Anammox process instable. Herein, with a mixture of landfill leachate and domestic sewage as wastewater, the effect on the properties of AnGS with two small particle size (0.1-0.2 mm) biochars (coconut and peach biochars) addition were investigated at different COD concentrations (150 mg·L^-1, 200 mg·L^-1, and 250 mg·L^-1), as well as at different BOD/TN (B/N) (0.3 and 0.5). Results showed that the nitrogen removal efficiencies decreased from 89 % to 72 % as the COD concentration increased by 100 mg·L^-1, while peach biochar reactor had better nitrogen removal performance. Excessive organic carbon supply inhibits AnAOB proliferation and B/N had the most significant effect on AnAOB (p < 0.05). The Polymerase Chain Reaction (PCR) indicated peach biochar reactor get higher activity of anammox-related functional genes (hzsA, hdh).

Nutrients removal from low C/N actual municipal wastewater by partial nitritation/anammox (PN/A) coupling with a step-feed anaerobic-anoxic-oxic (A/A/O) system

In this study, a novel combined strategy was successfully established by partial nitritation/anammox (PN/A) within a step-feed A/A/O process integrated with fixed-biocarriers to treat municipal sewage for 200 days. The excellent nutrients removal performance of this system compared with national level of discharging standard were achieved: low total inorganic nitrogen (7.1 mg/L) and phosphorus (0.3 mg/L) in the effluent with the influent (51.1 and 4.2 mg/L) at C/N ratios of 3.4 ± 0.5, mainly attributed to the stable PN (oxic zone) and subsequently anammox effect (anoxic zone). Nitrogen mass balance indicated that anammox contribution in anoxic zones to nitrogen loss could be up to 42% at stable phase. Therefore, aeration and carbon cost could be greatly reduced under low DO, low C/N and aerobic hydraulic retention time (HRT) of 7.4 h condition. The low DO and anammox bacteria retention in anoxic chambers promoted the washout of NOB and combination of anammox and partial nitritation process. During long-term operation, the activity of AOB effectively maintained while that of NOB drastically reduced to 0.1 mg N / g MLSS / h resulting in high and stable nitrite accumulation ratios (about 90%). The achievement of partial nitritation was mainly due to low DO (0.4-0.5 mg/L) and effective retention of anammox bacteria even with a low temperature (14.5 °C). Notedly, anammox activity gradually increased both on the biocarriers and in the flocs while a higher anammox abundance was observed on the biocarriers (2.48%) than that in suspend flocs (0.03%). As above, this study indicated that the novel combined strategies could be applicable to mainstream anammox, and a pilot-scale reactor will be established to verify and promote the industrial application of mainstream anammox.

Solar photo-assisted electrochemical processes applied to actual industrial and urban wastewaters: A practical approach based on recent literature

The application of electrochemical processes for wastewater treatment has increase significantly in the last two decades. However, most of the works are focused on lab-scale systems testing in saline simulated solutions spiked with a reference organic compound, evidencing the scarcity of studies on actual wastewaters through a more realistic practical approach. The aim of the present work is assessing the performance of electrochemical treatments in actual matrices, considering the formation of different oxidants species, apart from hydroxyl radicals, from dissolved ions contained in target effluents as well as both, the regeneration of Fe²⁺ and their combination with a light irradiation source. The degradation of a mix of microcontaminants in water matrices with different complexity by solar photoelectron-Fenton at natural pH and at pilot scale has been carried out at Plataforma Solar de Almería. Higher degradation rates were obtained when focusing on the more complex and saline matrices. In addition, complex industrial wastewaters mineralization was also studied by means of solar assisted electro-oxidation, showing the crucial role of ammonium concentration in the effluent, since it acts as a competitor for active chlorine species and so reducing the mineralization rate.

Ultrasensitive detection of amoxicillin by TiO2-g-C3N4@AuNPs impedimetric aptasensor: Fabrication, optimization, and mechanism

The trace amount of antibiotics in water can be enriched in the human body through the food chain, leading to extremely harmful effects on people's health. Therefore, it is urgent to develop new methods to detect trace pollutants in various aquatic phase. An analytical method utilizing the synergistic effect between the sensing strategy and catalytic material with high electron transfer capacity can be used to detect trace antibiotics. In this paper, an ultrasensitive impedimetric aptasensor was fabricated by the synergy between functionalized materials (TiO₂-g-C₃N₄) and gold nanoparticles (Au NPs). Due to the formation of the 'Au-S' bond between the thiol-aptamer and Au NPs, amoxicillin and the aptamer can be specifically recognized on the modified glassy carbon electrode (GCE), and the impedance signal increased rapidly. Meanwhile, the Box-Behnken Design (BBD) strategy was used to reduce the random error of the experiment, so that the prepared aptasensor has the highest sensitivity to the detection of amoxicillin. Under optimized conditions, the sensor successfully achieved the detection of amoxicillin in the ultra-low detection range (0.5-3 nM) and reached the ultra-low detection limit (0.2 nM). The detection strategy has good selectivity, reproducibility, and stability, and thus has good potential to detect amoxicillin in actual wastewater.

A highly efficient polyampholyte hydrogel sorbent based fixed-bed process for heavy metal removal in actual industrial effluent

High sorption capacity, high sorption rate, and fast separation and regeneration for qualified sorbents used in removing heavy metals from wastewater are urgently needed. In this study, a polyampholyte hydrogel was well designed and prepared via a simple radical polymerization procedure. Due to the remarkable mechanical strength, the three-dimensional polyampholyte hydrogel could be fast separated, easily regenerated and highly reused. The sorption capacities were as high as 216.1 mg/g for Pb(II) and 153.8 mg/g for Cd(II) owing to the existence of the large number of active groups. The adsorption could be conducted in a wide pH range of 3-6 and the equilibrium fast reached in 30 min due to its excellent water penetration for highly accessible to metal ions. The fixed-bed column sorption results indicated that the polyampholyte hydrogel was particularly effective in removing Pb(II) and Cd(II) from actual industrial effluent to meet the regulatory requirements. The treatment volumes of actual smelting effluent using one fixed bed column were as high as 684 bed volumes (BV) (7736 mL) for Pb(II) and 200 BV (2262 mL) for Cd(II). Furthermore, the treatment volumes of actual smelting effluent using tandem three columns reached 924 BV (31,351 mL) for Pb(II) and 250 BV (8483 mL) for Cd(II), producing only 4 BV (136 mL) eluent. Compared with the traditional high density slurry (HDS) process with large amount of sludge, the proposed process would be expected to produce only a small amount of sludge. When the treatment volume was controlled below 209.3 BV (7103 mL), all metal ions in the actual industrial effluent could be effectively removed (<0.01 mg/L). This wok develops a highly practical process based on polyampholyte hydrogel sorbents for the removal of heavy metal ions from practical wastewater.