Granular Sludge Using For Biological Phosphorus Removal From Wastewater And Phosphorus Recovery From Excess Sludge

Phosphorus is one of the most common pollutants that could cause water eutrophication. Meanwhile, phosphorus is also a kind of unsustainable and increasing shortage resources. Therefore, phosphorus recovery from wastewater is a meaningful strategy in order to realize phosphorus sustainable utilization.The technology of aerobic granular sludge was applied to enhanced biological phosphorus removal (EBPR) process from wastewater in this study. Phosphate-accumulating aerobic granules dominated by phosphate accumulating organisms (PAOs) were achieved in EBPR process operated under low organic loading rate. The cultured aerobic granules present good phosphorus removal performance and have numerous advantages such as higher phosphorus content and better settleability as compared to conventional activated sludge flocs in EBPR process. This result proved that aerobic granules could be obtained by controlling low organic loading rate.Low organic loading rate could decrease the microbial growth rate and increase the start-up time of the biological water treatment process. The influence of two-month storage under different conditions on the storage and subsequent reactivation performance of aerobic granules was investigated in order to validate the possibility that using cultured mature aerobic granules as seed sludge to speed up the formation of aerobic granules and reduce the start-up time. A specific inner rod-shaped bacteria aggregate tightly wrapped by filamentous bacteria structure provides phosphate-accumulating aerobic granules excellent storage performance. After two months storage, aerobic granules could maintain their structure integrity and quickly restored their original granular characteristics and phosphate removal ability. It was confirmed that low temperature and anaerobic storage conserve the structure integrity during storage and promote the reviving behaviors of phosphate-accumulating aerobic granules during reactivation.Effects of some parameters such as kinds of carbon resource etc. on phosphate-releasing performance of phosphate-accumulating aerobic granules were investigated. The optimal phosphate-releasing conditions were sodium acetic as carbon resource, 25℃and pH=7~8. The results suggested that the existence of nitrate could inhibit phosphate release of phosphate-accumulating aerobic granules when the carbon resource sodium acetic was deficient, which was due to the competition to the carbon resource between denitrification process and phosphate release process. It was discovered that sodium citrate could enhance the phosphate release of phosphate-accumulating aerobic granules. The influences of sodium citrate on the key enzymes'activities involving in ED and EMP pathway were investigated and the result confirmed that sodium citrate could enhance the phosphate release through mediating the metabolic pathway of glycogen.Heat treatment to sludge is an effective phosphate-releasing way. The phosphate, carbon and nitrogen release properties of phosphate-accumulating aerobic granules were investigated under different temperature. A combinative phosphate recovery process of heat treatment and anaerobic phosphate release was proposed by comparing their advantages and disadvantages. The organics released by the granules during heat treatment were used as the carbon resource for the granules during anaerobic phosphate release process, which decreased not only the cost of carbon resource addition during anaerobic phosphate release process but also the organics discharge after heat treatment. A steady model for this proposed phosphate recovery process was established based on the mass balance relationship and the model parameters were experimentally confirmed. The proposed phosphate recovery process was conducted to investigate the phosphate recovery performance. The results suggested that via this phosphate recovery process 59% phosphate released by the granules could be used for recovery, the mass of sludge discharge decreased 37.7% and the organics discharge decreased 43.5% as compared to that only via heat treatment.