Variation in humic and fulvic acids during thermal sludge treatment assessed by size fractionation, elementary analysis, and spectroscopic methods

Thermal pretreatment can be applied to sludge anaerobic digestion or dewatering. To analyze the variation in humic substances during thermal sludge treatment, sludge humic and fulvic acids were extracted before and after 30-min thermal treatment at 180℃, and then their contents, molecular weight distributions, elementary compositions, and spectral characteristics were compared. The results showed that the total contents of humic and fulvic acids in the sludge almost remained constant during thermal treatment, but 35% ofhumic and fulvic acids were dissolved from the sludge solids. Moreover, both humic and fulvic acids were partly decomposed and 32% of humic acids were converted to fulvic acids. The median value of the molecular weights of humic acids decreased from 81 to 41 kDa and that of fulvic acids decreased from 15 to 2 kDa. Besides the reduction in molecular size, the chemical structures of humic and fulvic acids also exhibited a slight change, i.e. some oxygen functional groups disappeared and aromatic structures increased after thermal sludge treatment.

Advances in Fe(Ⅲ)bioreduction and its application prospect for groundwater remediation:A review

Microbial Fe(Ⅲ)reduction is a significant driving force for the biogeochemical cycles of C,O,P,S,N,and dominates the natural bio-purification of contaminants in groundwater(e.g.,petroleum hydrocarbons,chlorinated ethane,and chromium).In this review,the mechanisms and environmental significance of Fe(Ⅲ)(hydro)oxides bioreduction are summarized.Compared with crystalline Fe(Ⅲ)(hydro)oxides,amorphous Fe(m)(hydro)oxides are more bioavailable.Ligand and electron shuttle both play an important role in microbial Fe(Ⅲ)reduction.The restrictive factors of Fe(Ⅲ)(hydro)oxides bioreduction should be further investigated to reveal the characteristics and mechanisms of the process.It will improve the bioavailability of crystalline Fe(Ⅲ)(hydro)oxides and accelerate the anaerobic oxidation efficiency of the reduction state pollutants.Furthermore,the approach to extract,culture,and incubate the functional Fe(Ⅲ)reducing bacteria from actual complicated environment,and applying it to the bioremediation of organic,ammonia,and heavy metals contaminated groundwater will become a research topic in the future.There are a broad application prospects of Fe(Ⅲ)(hydro)oxides bioreduction to groundwater bioremediation,which includes the in situ injection and permeable reactive barriers and the innovative Kariz wells system.The study provides an important reference for the treatment of reduced pollutants in contaminated groundwater.

Recovering humic substances from the dewatering effluent of thermally treated sludge and its performance as an organic fertilizer

The biologic treatment of the dewatering effluent from thermally treated sludge is difficult due to the high concentration of refractory humic substances. On the other hand, humic substances are an important source of organic fertilizer. In this study, a novel process using ferric coagulant was developed to recover humic substances from dewatering effluent for use as an organic fertilizer. When ferric coagulant was applied to raw dewatering effluent, up to 70% of humic substances were enmeshed by hydrolyzed ferric ions at an optimum pH of 4.5. The proper mass ratio of iron ions to humic substances was 0.6. In the recovered material, humic substances accounted for 24.2% of the total dry solids, and the amount of phosphorus （equivalent phosphorus pentoxide） was 6.2%. Heavy metals and other components all met the legal requirements for organic fertilizer. When the recovered material was applied to soybeans, the germination and growth of the seeds was significantly improved.