The enhancement of tetracycline degradation through zero-valent iron combined with microorganisms during wastewater treatment: Mechanism and contribution.

Ttetracycline (TC) posed potential threats to human health and ecological environment due to its mutagenicity, deformity and strong toxicity. However, few researches focused on the mechanism and their contribution of TC removal through microorganisms combined with zero-valent iron (ZVI) in wastewater treatment field. In this study, three groups of anaerobic reactors, added with ZVI, activated sludge (AS), ZVI coupled with activated sludge (ZVI + AS), respectively, were performed to explore the mechanism and the contribution of ZVI combined with microorganisms on TC removal. The results showed that the additive effects of ZVI and microorganisms improved TC removal. In ZVI + AS reactor, TC was mainly removed by the ZVI adsorption, chemical reduction and microbial adsorption. At the initial period of the reaction, microorganisms played a major role in the ZVI + AS reactors, contributing 80%. The fraction of ZVI adsorption and chemical reduction were 15.5% and 4.5%, respectively. Afterwards, the microbial adsorption gradually reached saturation and the chemical reduction as well as the adsorption of ZVI did their stuff. However, iron-encrustation covered on the adsorption sites of microorganisms and the inhibitory effect of TC on biological activity led to the decreasing TC removal in the ZVI + AS reactor after 23 h 10 min. The optimum reaction time for TC removal in ZVI coupling microbial system was about 70 min. In 1 h 10 min, the TC removal efficiencies were 15%, 63% and 75% in ZVI, AS and ZVI + AS reactors, respectively. Finally, in order to relieve the influence of TC on activated sludge and the iron cladding, a two-stage process was proposed to be explored later in the future.

Insights into Fe(â ¡)-sulfite-based pretreatment strategy for enhancing short-chain fatty acids (SCFAs) production from waste activated sludge: Performance and mechanism.

This paper proposed a concept of "co-treating" waste activated sludge (WAS) with waste-derived sulfite and environmentally-friendly ferrous iron. The maximal short-chain fatty acids (SCFAs) production from WAS anaerobic fermentation ascended by 27.1 times after pretreated by Fe(Ⅱ) activated sulfite with a sulfite dosage of 500 mg S/L and a Fe(Ⅱ)/sulfite ratio of 1.25. Mechanism explorations elucidated that the production of SO4·- and ·OH induced by Fe(Ⅱ)-activated sulfite-auto-oxidation remarkably promoted the disintegration of WAS and the biodegradability of dissolved organic matter, leading to enrichment of substances available for SCFAs-producing microbes. Besides, activities of hydrolytic and acidogenic enzymes were stimulated, while enzymes related to SCFAs consumption were inhibited severely. Further microbial community investigation confirmed that the abundances of hydrolytic microorganisms and acidogens were enriched. In addition, sludge dewaterability and vivianite production was enhanced after Fe(Ⅱ)-sulfite pretreated WAS fermentation, thereby benefiting the subsequent sludge disposal and resource recovery.

Evaluating the roles of coexistence of sludge flocs on nitrogen removal and nitrous oxide production in a granule-based autotrophic nitrogen removal system.

Certain levels of sludge flocs would always coexist in granule-based reactors due to the biomass detachment from granules. Such inevitable coexistence could affect both total nitrogen (TN) removal and nitrous oxide (N2O) production in autotrophic nitrogen removal systems. This work utilized a mathematical approach to systematically study the influence of the coexisting sludge flocs on TN removal and N2O production in a granular nitritation-anaerobic ammonium oxidation (Anammox) process for the first time, based on a 2-pathway N2O production model concept. The modelling results reveal that the highest TN removal efficiency decreases from ca. 87-88% to ca. 41-49% as the fraction of sludge flocs in the system increases from 10% to 40%, while the N2O production rate gradually increases with such increase. Meanwhile, both bulk dissolved oxygen (DO, 0.05-0.3 mg/L) and the size of granule (200-400 µm) could also influence the TN removal efficiency and N2O production. As the fraction of sludge flocs increases from 10% to 40%, the contribution of granular biomass to total N2O production is reduced due to increase of N2O-producing ammonia-oxidizing bacteria (AOB) in the sludge flocs, and the increase of granule size could intensify such decrease. In addition, the hydroxylamine oxidation pathway dominates the nitrifier denitrification pathway in both granules and sludge flocs under various testing conditions, whereas the increasing contribution of the latter would occur at a certain DO range, higher fraction of sludge flocs and smaller granule size. These results disclose an important influence of the coexisting sludge flocs on the performance of granular nitritation-Anammox systems.