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The high energy consumption associated with aeration, which is a widely used hydrodynamic method to mitigate membrane fouling in membrane bioreactors (MBR), poses a significant challenge to the widespread application of aerated MBR. In this study, low dissolved oxygen was applied to optimize the overall performance and reduce energy consumption in an anaerobic-anoxic-aerobic MBR (AAO-MBR) under fine and coarse bubble aeration conditions. Coarse bubble aeration exhibited better membrane fouling control, but induced releasing more proteins and polysaccharides in mixed liquor than that in fine bubble aeration. Coarse bubble aeration resulted in a decrease in the relative abundance of function bacteria, and there was a corresponding drop in enzymes involved in the nitrogen and phosphorus pathways. Furthermore, the average total specific energy demand (0.45 ± 0.02 kW·h/d) and total carbon emissions (0.32 ± 0.01 kg/d) of coarse bubble aeration was remarkably higher than that of fine bubble aeration (0.35 ± 0.01 kW·h/d and 0.25 ± 0.02 kg/d). Our results demonstrate that the fine bubble aeration in low dissolved oxygen-based AAO-MBR can optimize the overall performance and reduce energy consumption, thereby making it a more viable option for the wastewater treatment. © 2023

Invasive species and low dissolved oxygen (DO) threaten the biodiversity and ecosystem health of estuaries worldwide. To test the hypothesis that exposure to low DO reduces resistance of epifaunal community to invasion in the Chesapeake Bay, we conducted experiments using standardized settling panels, including 1) controlled experiments exposing epifaunal communities to low DO; 2) measurement of the short term response of motile and sessile epifauna to low DO; 3) survey of multiple sites in which community structure was correlated with low DO and other environmental variables; and 4) evaluation of the biological and structural effects of an invasive hydroid and a cryptogenic tunicate, both with high tolerance for low DO, on recruitment and development of epifauna. Periodic hypoxia was correlated with an increased cover of the native serpulid polychaete, Hydroides dianthus . Cover of invasive and cryptogenic species increased with exposure to moderate low DO. Cover and incidence of bryozoans, sabellid polychaetes, and cnidarians differed among DO treatments. Nematodes, caprellids, and harpacticoid copepods vacated epifaunal communities in response to low DO. In the multi-site survey, > 50% cover of invasive and cryptogenic species was associated with exposure to chronic low DO. Six of eight sites in the survey experienced periodic low DO (< 4 mg/l), but only one experienced chronic low DO ( > 40% of days below 4 mg/l DO). Shifting cover of Hydroides dianthus , barnacles, and invasive species was correlated (> 50%) with percent of days experiencing low DO. Epifaunal heterogeneity reflected environmental differences among sites. Species richness and diversity at local sites declined with increasing abundance of certain taxa in higher salinity, higher diversity areas. Heightened cover of Molgula manhattensis, Hydroides dianthus or barnacles led to reduced local diversity but regional

貧酸素と硫化水素がガザミ幼生に及ぼす影響を実験的に明らかにし、広島湾底層の観測結果から現場海域において海水中の溶存酸素と硫化水素がガザミ幼生に及ぼす複合影響を評価した。ガザミ幼生は48時間の硫化水素の暴露により、ゾエア期では≧5.2μgH2Sℓ-1、メガロパ期では≧9.5μgH2Sℓ-1、稚ガニ期では≧19.7μgH2Sℓ-1で生存率の有意な減少を示した。また、72時間の貧酸素条件によりゾエア期では≦3.4mgO2ℓ-1、メガロパ期では≦2.6mgO2ℓ-1、稚ガニ期では≦1.5mgO2ℓ-1で有意な生存率の減少が認められた。貧酸素と硫化水素の複合的条件下では、ゾエア期には≦3.4mgO2ℓ-1+≧5μgH2Sℓ-1の生存率は≦3.4mgO2ℓ-1の場合よりもさらに低下した。また、メガロパ期には≦3.4mgO2ℓ-1+10.1μgH2Sℓ-1および2.6mgO2ℓ-1+≧5.2μgH2Sℓ-1で、稚ガニ期には2.6mgO2ℓ-1+10.1μgH2S-1で、それぞれ貧酸素単独条件の場合よりも有意な生存率の減少を示した。広島湾奥部と江田内湾内の夏季の底層水中には、飽和度50%の低酸素水塊が認められ、10μgH2Sℓ-1以上の硫化水素濃度が検出された。以上の結果から、広島湾奥部と江田内湾内で、少なくともメガロパ期以前のガザミ幼生は鉛直移動により、底生期の稚ガニでは底生生活により底層水中の貧酸素と硫化水素に暴露されると考えられ、幼生期の自然減少が憂慮される。, Acute toxicity of hydrogen sulfide to larval stage of blue crab, Portunus trituberculatus was measured using a continous flow system. Survival rates of crab larvae to oxygen deficient water (DO≦3.4 mgℓ-1) and oxygen deficient water (3.4 mgO2ℓ-1 and 2.6 mgO2ℓ-1) with two different levels of hydrogen sulfide (10 μ-gH2Sℓ-1 and 5 μgH2Sℓ-1)were also determined. Survival rate of crab larvae exposed to hydrogen sulfide for 48 hours decreased at H2S≧5.2μgℓ-1, H2S≧9.5μgℓ-1, H2S≧19.7μgℓ-1 levels to zoea, megalopa and crab stage, respectively. Larval survival of zoea, megalopa and crab stage under low oxygen was significantly affected by DO≦3.4 mgℓ-1, DO≦2.6 mgℓ-1, 1.5 mgℓ-1 levels, respectively. The combined effects of low dissolved oxygen and hydrogen sulfide to the blue crab were stronger than each single effect. Namely, survival rate lowered under the combined exposure to≦3.4mgO2ℓ-1+≧5μgH2Sℓ-1, ≦3.4mgO2ℓ-1+10.1μgH2Sℓ-1, ≦2.6mgO2ℓ-1 +10.1μgH2Sℓ-1 levels to zoea, megalopa and crab stage larvae, respectively. The results of the field survey in Hiroshima Bay, Japan revealed that a part of the Bay was hypoxia (<3.2 mgℓ-1) in summer with high levels of hydrogen sulfide (≧10μgH2Sℓ-1)near the bottom. From these results, it could be concluded that the low levels of dissolved oxygen and high hydogen sulfide in the bottom water would affect the natural mortality of crab larvae in Hiroshima Bay.