Effect of different molecular weight organic components on the increase of microbial growth potential of secondary effluent by ozonation

Ozonation has been widely applied in advanced wastewater treatment. In this study, the effect of ozonation on assimilable organic carbon （AOC） levels in secondary effluents was investigated, and AOC variation of different molecular weight （MW） organic components was analyzed. Although the removal efflciencies were 47%-76% and 94%-100% for UV2s4 and color at ozone dosage of 10 mg/L, dissolved organic carbon （DOC） in secondary effluents was hardly removed by ozonation. The AOC levels increased by 70%-780% at an ozone dosage range of 1-10 mg/L. AOC increased significantly in the instantaneous ozone demand phase, and the increase in AOC was correlated to the decrease in UV254 during ozonation. The results of MW distribution showed that, ozonation led to the transformation of larger molecules into smaller ones, but the increase in low MW （〈1 kDa） fraction did not contribute much to AOC production. The change of high MW （〉100 kDa and 10-100 kDa） fractions itself during ozonation was the main reason for the increase of AOC levels. Furthermore, the oxidation of organic matters with high MWs （〉 100 kDa and 10-100 kDa） resulted in more AOC production than those with low MWs （1-10 kDa and 〈1 kDa）. The results indicated that removing large molecules in secondary effluents could limit the increase of AOC during ozonation.

Spatio-temporal variability in microfossil and geochemical records of Cenomanian-Turonian oceanic anoxic event-2:a review

The Cenomanian-Turonian boundary oceanic anoxic event(OAE-2;Bonarelli event;~94 Ma)is associated with a species turnover in the marine calcareous microfossil record,widespread marine anoxia,black shale deposition and positiveδ13C excursions.This study reviews 141 CTBE sites globally,aiming to understand micropaleontological,geochemical,and sedimentological expressions of OAE-2.There is a clear palaeogeographic and palaeobathymetric heterogeneity in the development of OAE-2 marine anoxia.A majority of the documented OAE-2 sites are from deep marine environments.The calcareous nannoplankton and benthic foraminifera record a diversity decline,while planktic foraminifera shows community level shifts and no major mass extinction.The variability of total organic carbon in OAE-2 sediments across sites(<1 to>10 wt.%)and theδ13C profiles(diachronous)have been attributed to different mechanisms of anoxia development.The increased primary“productivity model”gains support from productivity proxies(e.g.,Ba,P,Cu,Ni),redox-sensitive elements(e.g.,Mn,Mo,U,V,As),and eutrophic genera(e.g.,benthic foraminifera Gabonita spp.,calcareous nannofossils Biscutum spp.and Zeugrhabdotus erectus).The enhanced organic carbon“preservation model”in stratified(semi)restricted basins gains support from sites with lower enrichment of redox-sensitive elements and oligotrophic flora and fauna in the OAE-2 records.Geochronology of the Caribbean and the High Atlantic Large Igneous Province events(CLIP and HALIP)mark them as likely triggers of the OAE-2 related global perturbation of marine biogeochemistry.Volcanic triggers may have caused climate warming,altered hydrological cycles,enhanced continental weathering,shifts in ocean circulation,and nutrient flows.Addressing knowledge gaps,further research is urged,utilizing innovative proxies,and exploring underrepresented depositional systems to comprehensively understand OAE-2 onset and biotic crisis.