Evaluation of simultaneous organic matters and nutrients removal from municipal wastewater using a novel bioreactor (D-A2O) system

Modification of a plant-scale semi-centralized wastewater treatment system to enhance nitrogen and phosphorus removal from black water

Owing to the low ratio of chemical oxygen demand to total nitrogen (SCOD/TN), effective removal of nutrient pollutants from black water is difficult. In this study, to enhance nitrogen and phosphorus removal from such wastewater, a series of operational modification strategies was investigated and applied to a plant-scale semi-centralized system used for black water treatment. The results showed that 21 mg Fe³⁺/L was the optimal dosage for the chemical-enhanced pretreatment process, achieving average removal efficiencies of 51.1 and 74.1% for organics and phosphorus, respectively, with a slight enhancement in nitrogen removal by 2.3%. However, nitrogen and phosphorus removal could be further enhanced to 88 and 96%, by the addition of carbon sources in the post-anoxic zone of the reversed anaerobic-anoxic-aerobic process. Contrastingly, neither the addition of carbon sources in the pre-anoxic zone nor the prolongation of the time for pre-denitrification could significantly improve the nitrogen and phosphorus removal efficiencies. Furthermore, reducing the aeration intensity promoted simultaneous nitrification and denitrification in aerobic reactors, thereby making it a potential energy-saving method for system operation.

Unveiling organic loading shock-resistant mechanism in a pilot-scale moving bed biofilm reactor-assisted dual-anaerobic-anoxic/oxic system for effective municipal wastewater treatment

Microbial biomass and activity are frequently subjected to organic loading shock (OLS) from decentralized municipal wastewater. A hybrid moving bed biofilm reactor-assisted dual-anaerobic-anoxic/oxic system (D-A²MBBR) was established by integrating dual-anaerobic-anoxic/oxic with moving bed biofilm reactor to resist OLS for stable nutrients removal. The D-A²MBBR achieved 91.57% of chemical oxygen demand, 93.33% of ammonia-nitrogen, 80.20% of total nitrogen and 92.68% of total phosphorus removal, respectively, under the fluctuation of organic loading rate from 417.9 to 812.0 g COD m^-3 d^-1. The 16S rRNA gene sequencing revealed that Gemmobacter (7.28%) was identified as dominating anoxic denitrifying genus in oxic chamber, confirming the coexistence of aerobic and anaerobic/anoxic micro-environments. This circumstance boosted simultaneous nitrification-denitrification and phosphorus removal and the microbial community evolution inside the multilayer biocarrier-attached biofilms. In general, the D-A²MBBR was able to provide unique, cooperative and robust bacterial consortia to form a buffer against OLS, and ensuring effluent stability.

Role of carrier characteristics affecting microbial density and population in enhanced nitrogen and phosphorus removal from wastewater

This research aims to improve simultaneous nitrification-denitrification and phosphorus removal (SNDPR) using novel carriers and to demonstrate the effect of carrier characteristics on nutrient removal in a biofilm reactor. For this purpose, biofilms enriched with both polyphosphate-accumulating organisms (PAOs) and nitrifiers were cultivated in two parallel sequencing batch reactors containing conventional moving bed bioreactor carriers (MBBR) and a novel type of carriers (carbon-based moving carriers (CBMC)). The new carriers were produced based on recycled waste materials via a chemical-thermal process and their specific surface area were 10.4 times higher than typical MBBR carriers of similar dimensions. The results showed that the use of CBMC carriers increased bacterial adhesion by about 18.5% and also affected the microbial population inside the biofilms, leading to an increase in PAOs abundancy and thus an increase in biological phosphorus removal up to 12.5%. Additionally, it was corroborated that the volume of the anoxic zones with dynamic behavior is strictly influenced by the carrier structure and biofilm thickness due to a limitation in oxygen penetration. Accordingly, the formation of broader anoxic zones and shrinkage of these zones to a lesser extent resulted in the continuation of anoxic reactions for longer periods using the novel carriers. Thereby, an increase in nitrogen removal by about 15% was obtained mainly by denitrifying PAOs. The results also exhibited that a higher simultaneous nitrification-denitrification (SND) efficiency can be achieved by selecting an appropriate aeration program influencing the dynamic changes of anoxic zones. Overall, a biofilm system using the new carriers, with phosphorus and nitrogen removal efficiencies of 97.5% and 92.3%, was presented as an efficient, compact, and simple operation SNDPR process.

Occurrence and fate of pharmaceuticals in effluent and sludge from a wastewater treatment plant in Brazil

A wide variety of pharmaceuticals are discharged in water courses on a daily basis due to their incomplete removal from effluent in treatment plants. The aim of the current study was to assess the occurrence, fate and removal of pharmaceuticals from effluent and sludge samples collected in the biggest sanitary sewer plant in Southern Brazil. In total, 13 pharmaceuticals were detected in the influent through UHPLC-MS/M - paracetamol and caffeine recorded the highest concentrations, 137.98 and 35.29 µg L^-1, respectively. The treated effluent presented 11 compounds. Antibiotics were the class recording the widest diversity; metronidazole showed the lowest concentration (0.023 µg L^-1) and sulfamethoxazole presented the highest concentration (1.374 µg L^-1) in influent samples. Seven pharmaceuticals were absorbed by the sludge; among them, one finds caffeine, ciprofloxacin and ofloxacin, which were quantified both in the effluent and in the sludge. On the other hand, doxycycline, fenbendazole, norfloxacin and tetracycline were only detected in sludge samples - their concentrations ranged from 0.026 to 5.034 mg kg^-1. Clindamycin, oxytetracycline, sulfathiazole and trimethoprim concentrations increased throughout the treatment. There were high paracetamol and caffeine removal rates (>97%), and it may have happened due to degradation, photodegradation or chemical reaction. Ciprofloxacin and ofloxacin removal rate exceeded 83% mainly due to their sorption by sludge. Finally, the mass balance analysis highlighted high pharmaceutical loads (511.466 g d^-1) discharged into recipient waterbodies. This outcome demands broadening the removal of these pharmaceuticals from sewage.

Cost coupled removal efficiency analyses of activated sludge technologies to achieve the cost-effective wastewater treatment system in the meat processing units

This study was conducted to distinguish the most cost-effective activated sludge-based wastewater treatment technology by focusing on removal efficiency (RE) for applying in the meat processing units. Four different wastewater treatment plants (WWTPs), namely anaerobic/anoxic/oxic (A₂O), membrane bioreactor (MBR), moving bed bioreactor (MBBR), and integrated fixed-film activated sludge (IFAS) were simulated regarding the daily annual data obtained from a meat processing unit. The descending order concerning the total cost (TC) was as follows: MBR > A₂O > IFAS > MBBR while it was as MBR > IFAS > MBBR > A₂O based on RE. Regarding the energy and material consumption costs, the A₂O and MBR were the highest and lowest cost-effective systems, respectively. However, the MBR was the best from a biological treatment cost perspective. The boilers and co-generators contributed to 75% and 25% of the produced biogas, respectively, that supplied 50% of WWTP electricity demand. Among all different influent parameters, the effect of flow rate, COD, and BOD on the TC was statistically significant. Furthermore, the TC and present worth illustrated the most sensitivity to the construction cost alteration. This research provides insights into key economic parameters for a WWTP design and application.

Enhanced carbon and nitrogen removal in an integrated anaerobic/anoxic/aerobic-membrane aerated biofilm reactor system

A pilot-scale anaerobic/anoxic/aerobic-membrane aerated biofilm reactor (A2/O-MABR) system was constructed to enhance carbon and nitrogen removal. The effects of major operating parameters including the nitrate recycling ratio (R), sludge recycling ratio (r), and aerobic tank dissolved oxygen (DO) concentration on the system performance were investigated. The average removal efficiencies of the chemical oxygen demand (COD), ammonium nitrogen (NH4 +-N), and total nitrogen (TN) were 89.0 ± 3.2%, 98.8 ± 1.3%, and 68.5 ± 4.2%, respectively, and their effluent concentrations were averagely 22.6 ± 7.3, 0.32 ± 0.2, and 13.3 ± 1.2 mg L-1. The suspended sludge and biofilm in aerobic tank facilitated the simultaneous nitrification and denitrification (SND) processes. Indeed, unique biofilm layered structure and abundant microbial community in the biofilm on MABR would enhance nitrogen removal. Compared with the A2/O system, the A2/O-MABR system exhibited higher nitrifying bacteria oxygen uptake rate (OUR) of 58.1 and 54.5 mgO2 per gMLSS per h in suspended sludge and biofilm, respectively, and the lower mixed liquor suspended solid (MLSS) concentration of 1800 mg L-1. Moreover, high-throughput sequencing indicated that putative nitrogen removal bacteria such as Thauera and Paracoccus could be effectively enriched in the biofilm. Since the volume proportions of the anaerobic, anoxic, aerobic and settling tank in the existing A2/O system of the WWTP was not changed, the A2/O-MABR system was simple and practical for the upgrading of A2/O system.