Research On Augmentation Of Sludge Internal Carbon Release And Removal Of Nitrogen And Phosphorus In Hydrolysate

Volatile fatty acids(VFAs) are important intermediate products of sludge anaerobic hydrolysis and are biodegradable carbon sources. It is can be used as carbon source not only in biological nitrogen and phosphorus removal system, but also in biological process such as PHA synthesis. Therefore, emphasis has been put on how to take the sludge internal carbon. Hydrolysis is the key factor in utilization of the sludge internal carbon due to the hardness of breaking the cell walls of microbes during the hydrolysis process. Lysozyme can damage microbial cell walls and promote the hydrolysis of cells. In this paper, lysozyme was used to strengthen the release of sludge internal carbon. The releasing characteristics of VFAs, organic substances, nitrogen and phosphorus during the hydrolysis and acidification processes of excess activated sludge from domestic wastewater treatment plant were investigated respectively. By analyzing the effects of sludge concentration, temperature and pH value on the performance of sludge acid hydrolysis, the optimum hydrolysis conditions were determined. Under optimal hydrolysis condition, the effect of the lysozyme dosage on the excess sludge hydrolysis and acidification was discussed, and the nitrogen and phosphorus in hydrolysate was removed.The effect of sludge concentration on hydrolysis was discussed first without sludge pre-treatment. The hydrolysis was carried out under 30℃. It was found that dissolved organic matter, nitrogen and phosphorus in the liquid phase increased with the anaerobic hydrolysis time and was proportionally to the sludge concentration. The release of carbohydrate and protein was relatively high under 15000 mg/L sludge concentration, volatile acid production was close to that under 20000mg/L sludge concentration. At the same time the release of ammonia nitrogen and phosphate were lower. Therefore, the optimum sludge concentration for hydrolysis was determined as 15000mg/L. The anaerobic hydrolysis of non-pretreated exeess sludge under the sludge concentration of 15000mg/L was investigated at dieffrent temperature. The results showed that high temperature is favourable for substances release during hydrolysis process. SCOD, VFAs production were much higher under 35℃. The effect of pH value on hydrolysis under sludge concentration of 15000mg/L and treatment of 35℃was further investigated. The results showed that alkaline conditions were superior to acidic conditions. It can promote the production of VFAs, especially acetate and propionate. However, strong alkaline inhibited the formation of volatile acids, and pH 9 was selected as appropriate pH value.The hydrolysis performance under conditions of alkaline, presence of lysozyme and coupling lysozyme and alkaline were investigated respectively under the optimal conditions for hydrolysis. It was found that more water-soluble organic matter, nitrogen and phosphate and VFAs were released under coupling lysozyme and alkaline condition. The effect of lysozyme dosage on the hydrolysis was studied at pH 9, and it was found that 60mg/g sludge dosage of lysozyme is economical and reasonable.Finally, nitrogen and phosphorus in hydrolysate was removed through the formation of struvite (MgNH₄PO₄·6H₂O). It was found that a better removal of nitrogen and phosphorus were achieve when the mole ratio for Mg²⁺, NH⁴⁺ and PO₄^3- was l.2 : l : 1.