Carbon source recovery from waste sludge reduces greenhouse gas emissions in a pilot-scale industrial wastewater treatment plant

Carbon cycle regulation and greenhouse gas(GHG)emission abatement within wastewater treatment plants(WWTPs)can theoretically improve sustainability.Currently,however,large amounts of external carbon sources used for deep nitrogen removal and waste sludge disposal aggravate the carbon footprint of most WWTPs.In this pilot-scale study,considerable carbon was preliminarily recovered from primary sludge(PS)through short-term(five days)acidogenic fermentation and subsequently utilized on-site for denitrification in a wool processing industrialWWTP.The recovered sludge-derived carbon sources were excellent electron donors that could be used as additional carbon supplements for commercial glucose to enhance denitrification.Additionally,improvements in carbon and nitrogen flow further contributed to GHG emission abatement.Overall,a 9.1%reduction in sludge volatile solids was achieved from carbon recovery,which offset 57.4%of external carbon sources,and the indirect GHG emissions of the target industrial WWTP were reduced by 8.05%.This study demonstrates that optimizing the allocation of carbon mass flow within a WWTP has numerous benefits.

Characterization of changes in extracellular polymeric substances and heavy metal speciation of waste activated sludge during typical oxidation solubilization processes

Biopolymer solubilization is considered to be the rate-limiting stage of anaerobic digestion of waste activated sludge(WAS). Oxidation processes have been proven to be effective in disrupting sludge flocs and causing solubilization of the solid biopolymers. In this study,WAS was treated by NaNO2 or H2 O2 oxidation at p H of 2. The changes in extracellular polymeric substances properties and the speciation of heavy metals were investigated. The results revealed that both NaNO2 and H2 O2 treatments were effective in solubilizing organics in WAS, while the conversion of biopolymers in the two treatment processes was different. Free nitrous acid destroyed the gel network structure of EPS, and organic materials were released from the solid phase to the supernatant. Indigenous peroxidase catalyzed H2 O2 to produce hydroxyl radicals which caused significant solubilization of biopolymers, and the protein-like substances were further degraded into micro-molecule polypeptides or amino acids at high dosages of H2 O2. During the oxidation processes, Zn, Cd and Cu, with excellent mobility, tended to migrate to the supernatant, and thus were easy to remove through the liquid–solid separation process. Ni and As showed moderate migration ability, of which the residual fraction tended to transform into reducible and soluble fractions. With poor mobility, Cr and Pb mainly existed in the forms of residual and oxidizable fractions, which were difficult to dissolve and remove from WAS. Both NaNO2 and H2 O2 treatment resulted in the enhancement of sludge solubilization efficiency and heavy metal mobility in WAS, but different heavy metals showed distinct migration and transformation behaviors.

Preparation of ultrahigh-surface-area sludge biopolymers-based carbon using alkali treatment for organic matters recovery coupled to catalytic pyrolysis

In this work,we employed waste activated sludge(WAS)as carbon source to prepare ultrahigh specific surface area(SSA)biopolymers-based carbons(BBCs)through alkali(KOH)treatment coupled to pyrolysis strategy.Before the pyrolysis process,the involvement of KOH made a great recovery of soluble biopolymers from WAS,resulting in highly-efficient catalytic pyrolysis.The Brunner-Emmett-Teller and pore volume of BBCs prepared at 800℃(BBC800)reached the maximum at 2633.89 m2·g-1 and 2.919 m3·g-1,respectively.X-ray photoelectron spectroscopy suggested that aromatic carbon in the form of C=C was the dominant fraction of C element in BBCs.The N element in BBCs were composed of pyrrolic nitrogen and pyridinic nitrogen at 700℃,while a new graphitic nitrogen appeared over 800℃.As a refractory pollutant of wastewater treatment plants,tetracycline(TC)was selected to evaluate adsorption performance of BBCs.The adsorption behavior of BBCs towards TC was conformed to the pseudo-second-order kinetic and the Langmuir models,signifying that chemisorption of monolayers was dominant in TC adsorption.The adsorption capacity of BBC800 reached the maximum at 877.19 mg·g-1 for 90 min at 298 K.Thermodynamic analysis indicated that the adsorption process was endothermic and spontaneous.Hydrogen bonding andπ-πstacking interaction were mainly responsible for TC adsorption,and interfacial diffusion was the main rate-control step in adsorption process.The presence of sol-uble microbial products(SMPs)enhanced TC removal.This work provided a novel strategy to prepare bio-carbon with ultrahigh SSA using WAS for highly-efficient removal of organic pollutants.