Study On Carbon Source Recovery From Food Wastes And Nitrogen Removal Enhancement

Based on the two big problem about insufficient carbon source for nitrogen removal in the wastewater treatment process and dispoal difficulty for food wastes, carbon source recovery and application from food wastes anaerobic fermentation technology were investigated in the study under the principle of turing “wastes” into “treasures”. In this paper, firstly the physicochemical properties of campus food wastes were studied, then short-term free anaerobic fermentation technology from food wastes and operational conditions optimization were investigated to improve carbon sourec recovery efficiency. Also the organic component of fermentation liquid from food wastes was analysed. The denitrification performance of fermentation liquid was evaluated by batch denitrification experiments and obtained competitive denitrification performance with common chemical carbon sources. For wastewater with lower COD/N ratio, the nitrogen removal enhancement when using two supplementary carbon source(fermentation liquid and sodium acetate) were compared by experiments using sequencing batch reactors(SBRs), meanwhile the effect of influent carbon source on metabolic potential of microorganisms was also studied. As a multi-organic mixture, fermentation liquid seem to be high-quality external carbon source for enhancing nitrogen removal for wastewater with low COD/N ratio.By continuous samling and detecting, the physicochemical properties of campus food wastes and substrate feasibility as anaerobic fermentation process were evaluated. The campus food wastes have stable composition and abundant organics content, mainly including of carbohydrate, protein and lipid, and their average content were about 61.4%,9.8% and 9.2%, respectively. And the substrate degradation potential value of food wastes was predicted as 173.1 mlH2/gVS and 520 mlCH4/gVS.By anaerobic fermentation experiments, the soluble carbon source recovery by short-term free anaerobic fermentation from food wastes were studied, meanwhile optimizing the operational conditions. The short-term free fermentation process resulted in maximum soluble carbon source recovery efficiency and minimum biogas loss. By investigating the effect of temperature and initial solid concentration on substrate degradation and soluble carbon source production, the optimal operation conditions were obtained as room temperature and solid concentration of 13% because of maximum soluble carbon source concentration as 67.6 gCOD/L and organics transformation rate: hydrolysis(37.6%), acidogenesis(9.9%) and biogas(15.6%). The effective soluble carbon source was recovered for 0.376 gSCOD/gTCOD and 0.096 g SCOD/g substrate by short-term free fermentation technology. And the soluble carbon source was a multi-organics system including of carbohydrate, organic acids mainly including of dominating lactic acid and acetic acid and some undefined organics.By batch denitrification experiments, the denitrification performance were evaluated when using fermentation liquid as carbon source, and the denitrification performance(with a denitrification rate of VDN=12.89 mgN/gVSS.h and a denitrification potential of PDN=0.174 gN/gCOD) could be achieved. In the fermentation liquid, not only the lactic and acetic acids, as low molecular weight organics, were readily utilized by microorganism, but also carbohydrate and other undefined organics, as big molecular weight organics, were slowly utilized by denitrifying bacteria. By comparing with glucose and sodium acetate, two commonly used chemical carbon sources, fermentation liquid showed a denitrification result similar to sodium acetate but much better than glucose.In order to enhance nitrogen removal from domestic wastewater with a low, the effect of fermentation liquid as supplementary carbon source for wastewater with low carbon/nitrogen(C/N) ratio was evaluated by experiments using sequencing batch reactors(SBRs). The total nitrogen removal increased by about 25% in contrast to the 20% brought about by the addition of sodium acetate. In order to characterize the metabolic potential of microorganisms by utilizing different carbon sources, Biolog-ECO tests were conducted with activated sludge samples from the SBRs. As a result, in comparison with sodium acetate, the sludge sample by fermentation liquid addition showed higher microbial diversity indexes and metabolic potential.In this study, the short-term free fermentation process from food waste was demonstrated as an effective way for carbon source recovery and for enhancing nitrogen removal in biological nutrients removal process. All these results could provide theory base for food wastes dispose and reuse for biological nitrogen removal.