富磷污泥厌氧发酵过程中乙酸浓度对磷释放的影响

以强化生物除磷(EBPR)污泥为研究对象,考察了不同初始乙酸浓度条件下富磷污泥厌氧发酵过程中磷及相关指标的变化,并探讨释磷机制.结果表明:初始乙酸浓度对污泥最大释磷量影响不大,(73.1±2.2)%的污泥总磷量(TP)以磷酸盐的形式释放到液相中,其主要来自聚磷的分解.聚磷的分解途径包括:1)聚磷菌(PAOs)通过吸收乙酸贮存聚β-羟基烷酸酯(PHA)的厌氧生物释磷机制释放磷酸盐;2)PAOs的维持作用导致的聚磷直接分解过程.当初始乙酸浓度不充足时,生物释磷过程受限制,聚磷以相对较慢的速率直接分解;随着乙酸浓度的增大,生物释磷速率增快,同时随之增加的PHA含量能促进污泥的水解酸化.上清液中PO43--P和Mg2+浓度在达到最大值后出现了下降的现象,其可能形成鸟粪石等沉淀.根据试验数据,本文提出了从富磷污泥中回收磷的策略,即可在厌氧消化开始前向污泥中投加一定量碳源,并在发酵24h内分离上清液进行磷回收,这样不仅可以快速大量地从上清液中回收磷并减少沉淀引起的管道堵塞等问题,还可消除高浓度磷酸盐对厌氧消化的影响.

Effect of acetate concentration on phosphate release during anaerobic fermentation of phosphorus-rich sludge

Experiments were carried out to investigate phosphate release mechanism according to the variations of phosphate and related parameters during anaerobic fermentation of enhanced biological phosphorus removal (EBPR) sludge in the presence of different initial acetate concentrations. The results indicated that the initial acetate concentration did not significantly affect the maximum level of the released phosphate concentration. During the fermentation, (73.1±2.2) % of total phosphorus (TP) could be released in the form of phosphate into liquid phase, and it was mainly from the decomposition of polyphosphate. The decomposition pathways of polyphosphate include: 1) Anaerobic biological phosphorus release mechanism that polyphosphate accumulating organisms (PAOs) take up acetate and store it as polyhydroxyalkanoate (PHA); 2) direct decomposition of polyphosphate due to PAOs maintenance. When the initial acetate was insufficient, biological phosphorus release was limited and polyphosphate was decomposed in a relatively slow rate. When the acetate concentration increased, the biological phosphate release rate increased. Moreover, the increased content of PHA accelerated sludge hydrolysis and acidification. PO43--P and Mg2+ concentrations slightly decreased after their maximum levels were reached, because they were precipitated probably in the form of struvite. According to the above results, strategy for recovering phosphorus from phosphorus-rich sludge is proposed: adding some carbon source before sludge anaerobic digestion so as to recover phosphate from the separated supernatant within 24h of anaerobic fermentation. Thus, it can not only speed up and maximize phosphate release and minimize the block of pipes due to precipitation, but also avoid the inhibition of high phosphate concentration on anaerobic digestion.