游离氨调控对污泥高含固厌氧消化反应器性能的影响

污泥高含固厌氧消化系统中,过高的游离氨(free ammonia nitrogen,FAN)浓度被认为是影响其产气性能的主要因素之一.通过降低pH和提高总氨氮(total ammonia nitrogen,TAN)浓度两种方法,考察了进料含固率为15%的中温半连续污泥高含固厌氧消化反应器在这两种游离氨调控措施下的性能表现.结果表明,随着TAN的提高,FAN从(400±174)mg·L~(-1)提升至(526±25)mg·L~(-1),日产沼气量从(11.9±0.3)L·d-1降低到(10.3±0.2)L·d-1,挥发性固体(volatile solid,VS)降解率降低了33.7%;同时,当通过降低pH使得FAN从(330±99)mg·L~(-1)下降至(47±13)mg·L~(-1)时,日沼气产量也从(14.4±1.1)L·d-1下降到(10.8±0.3)L·d-1,VS降解率降低了26.9%,系统性能并没有随着FAN的下降而提升.随着pH调控的停止,游离氨浓度逐步回升至300 mg·L~(-1),系统性能也恢复至调控之前的水平,表明pH调控的过程产生了游离氨浓度控制之外的抑制性作用.最后,通过对细菌和古菌的多样性分析以及甲烷菌的定量PCR分析,可以发现两个反应器系统产气性能的变化都伴随着细菌种群结构的明显变化.污泥高含固厌氧消化系统中过高的FAN(500 mg·L~(-1))使得降解蛋白的细菌的主要种群由Tepidimicrobium和Proteiniborus转变为Anaerobranca.而通过降低pH来控制游离氨浓度之后,一些糖类和蛋白质类发酵细菌的活性也受到影响,并导致这些物质水解效率的下降,进而由于产甲烷菌的基质供给量的不足而削弱系统的产气性能.

Effects of Free Ammonia Regulation on the Performance of High Solid Anaerobic Digesters with Dewatered Sludge

High free ammonia nitrogen (FAN) is regarded as a main factor that inhibits biogas production in high solid anaerobic digestion systems with dewatered sludge. Two mesophilic semi-continuous anaerobic digesters fed with dewatered sludge (input total solids=15%) were operated and their performance under different FAN concentrations by two regulation methods including pH reduction and total ammonia nitrogen (TAN) promotion were investigated. Results showed that when FAN was elevated from (400±174) mg·L^-1 to (526±25) mg·L^-1 with the increase of TAN, the daily biogas yield declined from (11.9±0.3) L·d^-1 to (10.3±0.2) L·d^-1. Meanwhile, volatile solids (VS) reduction rate decreased by 33.7%. When FAN dropped from (330±99) mg·L^-1 to (47±13) mg·L^-1 due to pH reduction, daily biogas yield declined from (14.4±1.1) L·d^-1 to (10.8±0.3) L·d^-1 and VS reduction rate decreased by 26.9%. The system performance was not enhanced with the reduction of FAN. With the stop of pH regulation, FAN gradually raised again to 300 mg·L^-1 and digester performance recovered to the same as the situation before regulation. The result suggested that inhibition occurred during pH reduction. By 16S rRNA pyrosequencing analysis on bacterial and archaeal diversity and quantitative PCR analysis aiming at methanogens, it was found that bacterial community structure both changed obviously with obvious performance decline in the two digesters. Excessive FAN (>500 mg·L^-1) could change the main bacteria species which degrade protein from Tepidimicrobium and Proteiniborus to Anaerobranca. On the other hand, some carbohydrate and protein degrading bacteria were also inhibited by pH reduction for FAN control, leading to the decline of hydrolysis rates of organic matters. As a result, the shortage of substrate supply for the methanogens weakened the biogas production of the digestion system.