Iron-based mixotrophic denitrification for enhancing nitrate removal from municipal secondary effluent: Performance, microbial community dynamics, and economic feasibility.

High nitrate content limits the recycling of the secondary effluent of wastewater treatment plants. In the research, one biomass-iron mixture (BIM) filter material based on mixotrophic denitrification mode (heterotrophic and iron-driven autotrophic denitrification) was developed and used to construct a novel denitrification biological filter (BIM-DNBF) for the nitrogen removal of secondary effluent. BIM-DNBF had a short start-up time (approximately 9 days), and high total nitrogen removal (81 %-89 %) without external addition of organic carbon sources during the whole operation. The coexistence of dominant heterotrophic-denitrification-like Pseudomonas and Erysipelothrix as well as iron-driven autotrophic-denitrification-like Citrobacter, Acidovorax, etc. were found in the BIM-DNBF. Moreover, biomass was recognized as one key player in promoting the reduction of Fe3+ to Fe2+, thereby facilitating the occurrence of iron-driven autotrophic denitrification. In addition, BIM-DNBF was assessed to be affordable. These findings provide evidence that BIM-DNBF can be an efficient technology for nitrogen removal of secondary effluent.

Assessment and analysis of aged refuse as ammonium-removal media for the treatment of landfill leachate.

This is the first attempt to explore the sustainability of aged refuse as ammonium-removal media. Batch experiments combined with the aged-refuse-based reactor were performed to examine how the adsorption and desorption processes are involved in the ammonia removal via aged refuse media in this research. The results showed that the adsorption of ammonium by aged refuse occurred instantly and the adsorbed ammonium was stable and less exchangeable. The adsorption data fit the Freundlich isotherms well and the n value of 0.1-0.5 indicated that the adsorption of ammonium occurred easily. The maximum adsorbed ammonium occupied less than 10% of the cation exchange capacity in aged-refuse-based reactors owing to the high solid/liquid ratios (50:1-120:1). The synergistic transformations of ammonium within the aged-refuse-based reactor indicated that the cation exchange sites only provide temporary storage of ammonium, and the subsequent nitrification process can be considered the predominant restoration pathway of ammonium adsorption capacity of the reactor. It seems reasonable to assume that there is no expiry for the aged-refuse-based reactor in terms of ammonium removal owing to its bioregeneration via nitrification.

Field assessment of stratified aged-refuse-based reactor for landfill leachate treatment.

The aim of this study was to investigate the engineering applicability of the stratified aged-refuse-based process for landfill leachate treatment. In this work, a pilot-scale (10m(3)day(-1)) and a demonstration-scale (200m(3)day(-1)) stratified reactor, containing the aged refuse excavated from an 8-year-old closed landfill cell, were used as a medium by which to treat landfill leachate generated in the Shanghai Refuse Landfill (SRL). The preliminary-treated leachate with initial CODcr, NH(3)-N and total-N concentrations of 2387-8592, 1431-2145 and 1290-2188 mgL(-1), respectively, was intermittently sprayed over the refuse surface eight times a day with 3 h per interval in the pilot study. The results from the pilot operation showed that on average 89.5% of COD, 98.8% of NH(3)-N and 52.6% of total N could be removed from a hydraulic load of 0.267-0.444m(3)m(-3)refuseday(-1). Additionally, similar results were observed for the demonstration system even with the leachate of low BOD(5)/COD ratios (0.17-0.19). The investment and operational costs of this stratified process were about 20000yuan (€2200) and 1-2 yuan (€0.11-0.22) per m(3) leachate treated, respectively. Taken together, the stratified process has some significant advantages including low operation cost, easy maintenance and good adaptability to the leachate of variable quality, which makes this process a viable alternative for the treatment of landfill leachate.