Long-term Effects Of Ni(Ⅱ) On Activated Sludge In SBR System

Five identical4-L sequencing batch reactors （SBRs） were constructed to systematicllyinvestigate the long-term effects of Ni（Ⅱ） on them. The effects of Ni（Ⅱ） on substrate removaland microorganism activity were studied, and an indicator which would be used tocharacterize the effects of Ni（Ⅱ） on the community diversity of activated sludge wasconfirmed. The accumulation and fraction distribution of Ni（Ⅱ） in sludges were also determined toevaluate their effects on the performance of SBRs. Additionally, the relationships among all ofperformance, substrate removal, microorganism activity, and community diversity ofactivated sludge during the whole wastewater treatment process had been comprehensivelydiscussed. The main experimental conclusions obtained from this study are listed as follows.（1） With the increasing of Ni（Ⅱ）-feeding concentration, the effluent pH valuesnon-significantly increased, while the turbidity （TUR） and electrical conductivity （EC） ofSBR systems obviously increased during the operating periods. And it was seen that the TURand EC had a little improvement in SBRs during the recovery.（2） Ni（Ⅱ） could significantly inhibited the total organic carbon （TOC） and NH₄⁺-Ndegradation abilities of SBR systems, and the influence on NH₄⁺-N degradation ability wasgreater than TOC. Compared to the control system （CK）, no significant reduction in the TOCand NH₄⁺-N removal efficiencies were found in the SBR systems feeding with lowconcentrations (<5mg·L^-1) of Ni（Ⅱ）. However, significant reductions could be observed inthe TOC and NH₄⁺-N removal efficiencies with the increasing of Ni（Ⅱ）-feedingconcentration.（3） Low concentrations (<5mg·L^-1) of Ni（Ⅱ） could improve the INT-ETS activity ofactivated sludge microorganisms, while the improvements could not be seen for sOUR andTTC-ETS activity. With the increasing of Ni（Ⅱ）-feeding concentration, the sOUR, INT-ETSand TTC-ETS continuously increased, and the effects of Ni（Ⅱ） could quickly inhibit theactivities in a short time. No significant improvements were seen after termination of theNi（Ⅱ）-feeding. Additionally, INT-ETS is superior to sOUR and TTC-ETS in its ability todetect the toxic effects of Ni（Ⅱ） on sludge microorganisms activity owing to its highersensitivity, lower toxicity to microorganisms, easier biodegradability, smaller effects of O2,more reproducible measurements, and easier extraction procedure.（4） Ni（Ⅱ） could significantly affect the carbon utilization capacity of the activated sludge microorganisms. Low concentrations (<5mg·L^-1) of Ni（Ⅱ） could improve the carbonutilization capacity of the activated sludge microorganisms, while high concentrations (>10mg·L^-1) of Ni（Ⅱ） could inhibit that. It could be observed that a significant influence of Ni（Ⅱ）on the metabolic function of activated sludge microbial community, while non-significantinfluence on functional diversity of activated sludge microorganism. The carbohydrates,carboxylic acids and polymers were the main carbon substrates for activated sludge microbialcommunities.（5） With the increasing Ni（Ⅱ）-feeding concentrations, non-significant difference ofelectrical conductivity （EC） values could be identified among these sludges obtained fromSBRs, while obviously decrease of the loss on ignition （LOI）, total contents of nitrogen （TN）and phosphorus （TP） of sludges could be obtained, and total content and sum of four fractionsof Ni（Ⅱ） increased. The predominant fraction of Ni（Ⅱ） accumulated in sludge was theexchangeable/acid soluble fraction （F1）, and the sum of the exchangeable/acid solublefraction （F1） and reducible fraction （F2） accounted for75.8⁹0.0%of the total Ni（Ⅱ）,indicating the relatively high mobility and bioavailability of Ni（Ⅱ） in these sludges. Theoxidizable fraction （F3） may contribute to a more important effect to sludge microorganismsthan other chemical fractions of Ni（Ⅱ） in sludges. Additionally, the comparative analysis ofFT-IR showed that the structure of sludges had undergoned some changes after the feeding ofNi（Ⅱ）.（6） Except two or three individual indicators, the performance, substrate removal ofSBRs, and microorganism activity, community diversity, physical and chemical properties ofactivated sludge, could characterize mutually, and they could all serve as effective indicatorsfor predicting the content and long-term effects of Ni（Ⅱ） on the SBR systems.