Abstract
A strain was isolated from biological sludge to produce EPS by using anaerobically digested swine wastewater (ADSW). Potential of the EPS in ADSW treatment were discussed. Results showed that the optimal fermentation medium for EPS production was determined as 4 g K2HPO4, 2 g KH2PO4, and 2 g sucrose dissolved in 1 L ADSW. After fermentation for 60 h, 2.98 g EPS with main backbone of polysaccharides can be extracted from 1 L of fermentation broth. The EPS showed good performances in ADSW treatment, after conditioned by this EPS, removal efficiencies of COD, ammonia, and TP reached 70.2%, 76.5% and 82.8%, respectively, which were higher than that obtained when chemicals were selected as conditioning agents. Removal efficiencies were further improved when the EPS and polyaluminum chloride (PAC) were used simultaneously, and finally reached 91.6%, 90.8%, and 92.5%, respectively, under the optimized conditioning process by the composite of EPS of 16 mg/L, PAC of 12 g/L, pH of 7.5, and agitation speed of 200 r/min.
Highlights
Extensive swine breeding has already been highlighted as an effective way to increase meat production efficiency in China[1], and a large quantity of swine wastewater was generated[2], which would adversely affect agricultural development and environmental quality as well as people’s lives if disposed without sufficient treatment[3]
The extracellular polymeric substances (EPS) showed good performances in anaerobically digested swine wastewater (ADSW) treatment, after conditioned by this EPS with a dose of 20 mg/L and a pH condition of 7.5, removal efficiencies of chemical oxygen demand (COD), ammonia, and total phosphorus (TP) reached 70.2%, 76.5% and 82.8%, respectively, which were much better than the ones obtained with chemicals
Due to the high molar weight and polar groups, the EPS can supply ample binding sites, strong bridging, and strong van der Waals forces for suspended solids in ADSW, and suspended solids can be adsorbed to EPS molecular chains to settle rapidly, far improved the removal of COD, ammonia, and TP from ADSW31
Summary
Extensive swine breeding has already been highlighted as an effective way to increase meat production efficiency in China[1], and a large quantity of swine wastewater was generated[2], which would adversely affect agricultural development and environmental quality as well as people’s lives if disposed without sufficient treatment[3]. Yang et al optimized the flocculation conditions for kaolin suspension using the composite flocculant of MBFGA1 and PAC by response surface methodology[10], Guo et al enhanced dewatering of sludge with the composite of a bioflocculant and P(AM-DMC)[11] In these two researches, the flocculating activity of kaolin suspension and the sludge dewatering ability were improved by using the composite, while the PAC and P(AM-DMC) doses were decreased, compared with their use alone. The flocculating activity of kaolin suspension and the sludge dewatering ability were improved by using the composite, while the PAC and P(AM-DMC) doses were decreased, compared with their use alone In this case, it is feasibility and meaningful to enhance the treatment of ADSW by the compound uses of chemicals and EPS. RSM, a statistical technique for building multivariable equation and evaluating their optimal values, can be effectively used to investigate the interactions of chemicals and EPS in the treatment of ADSW
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