Emerging wastewater treatment strategy for efficient nitrogen removal and compact footprint by coupling mainstream nitrogen separation with chemical coagulation and biological aerated filter

A review of iron use and recycling in municipal wastewater treatment plants and a novel applicable integrated process

Chemical methods are expected to play an increasingly important role in carbon-neutral municipal wastewater treatment plants. This paper briefly summarises the enhancement effects of using iron salts in wastewater and sludge treatment processes. The costs and environmental concerns associated with the widespread use of iron salts have also been highlighted. Fortunately, the iron recovery from iron-rich sludge provides an opportunity to solve these problems. Existing iron recovery methods, including direct acidification and thermal treatment, are summarised and show that acidification treatment of FeS digestate from the anaerobic digestion-sulfate reduction process can increase the iron and sulphur recycling efficiency. Therefore, a novel applicable integrated process based on iron use and recycling is proposed, and it reduces the iron salts dosage to 4.2 mg/L and sludge amount by 80%. Current experimental research and economic analysis of iron recycling show that this process has broad application prospects in resource recovery and sludge reduction.

Performance evaluation and energy potential analysis of anaerobic membrane bioreactor (AnMBR) in the treatment of simulated milk wastewater

An anaerobic membrane bioreactor (AnMBR) was employed as primary treatment unit for anaerobic treatment of simulated wastewater to produce high effluent quality. A lab scale hollow fiber membrane was used to scrutinize the performance of AnMBR as a potential treatment system for simulated milk wastewater and analyze its energy recovery potential. The 15 L bioreactor was operated continuously at mesophilic conditions (35 °C) with a pH constant of 7.0. The membrane flux was in the range of 9.6-12.6 L/m². h. The different organic loading rates (OLRs) of 1.61, 3.28, 5.01, and 8.38 g-COD/L/d, of simulated milk wastewater, were fed to the reactor and the biogas production rate was analyzed, respectively. The results revealed that the COD removal efficiencies of 99.54 ± 0.001% were achieved at the OLR of 5.01 gCOD/L/d. The highest methane yield was found to be at OLR of 1.61 gCOD/L/d at HRT of 30 d with the value of 0.33 ± 0.01 L-CH₄/gCOD. Moreover, based on the analysis of energy balance in the AnMBR system, it was found that energy is positive at all the given HRTs. The net energy production (NEP) ranged from 2.594 to 3.268 kJ/gCOD, with a maximum NEP value of 3.268 kJ/gCOD at HRT 10 d HRT. Bioenergy recovery with the maximum energy ratio, of 4.237, was achieved with an HRT of 5 d. The study suggests a sizable energy saving with the anaerobic membrane process.

Effects of organics concentration on the gravity-driven membrane (GDM) filtration in treating iron- and manganese-containing surface water

Iron and manganese contamination in the surface water is posing great challenges to the drinking water treatment supply, especially in the complex cases of organics involvement. Gravity-driven membrane (GDM) filtration equipped with the dual functions of ultrafiltration and biocake layer, conferred promising potentials in the removals of iron and manganese. This study evaluated the effects of organics concentrations on the removal performance of iron and manganese, as well as on the flux stabilization during GDM long-term filtration. The results indicated that stable flux level and the removal efficiency of manganese initially increased with the increase of organics concentration in the feed water, and then decreased. The moderate concentration of organic compounds in the feed water would positively facilitate the microbial activities and benefit to engineering a heterogeneous and porous biocake layer on the membrane surface, contributing to the highest improvements of stable flux (6.3 L m^-2 h^-1), while high concentration of organic compounds in the feed water would result in the increase in the thickness and EPS concentration of the biocake layer, leading to a flux reduction. Furthermore, the moderate concentration of organic compounds in the feed water was also beneficial to the manganese removal (> 94.6%) due to the more accumulation of auto-catalytic oxidation manganese oxides (MnOx) within the biocake layer and the improved biological degradation, however, further increase of organics concentration would deliver a negative impact on the manganese removal owing to the wrapping of MnOx by the organic substances. Overall, these findings provide practical and acceptable strategies to the selections of pre-treatments prior to GDM and promote its extensive application in treating the iron- and manganese-containing surface water.