蛋白酶K对厌氧消化系统EPS产生特性及消泡潜能的影响

Effect of proteinase K on extracellular polymeric substances production and defoaming potential in the anaerobic digestion system of food waste

起泡是厨余垃圾厌氧消化过程中常见的操作难题,高效消泡方法的开发备受关注.先前研究表明胞外聚合物(EPS)是起泡的诱因,其中的疏水性蛋白组分更与泡沫形成直接相关.在此背景下,本研究向厌氧消化系统中添加不同剂量的蛋白酶K,以期探索其对厨余垃圾厌氧消化系统EPS产生特性及消泡潜能的影响.结果表明,蛋白酶K对厌氧消化微生物没有生物毒性,添加0.2 mg·g^(-1) TS蛋白酶K后系统甲烷产率反而比对照组高12.35%±3.36%.此外,蛋白酶K可以有效降低厨余垃圾厌氧消化系统的起泡趋势和泡沫稳定性,具有作为消泡剂的潜质.蛋白酶K的添加改变了EPS的产生特性,促进了溶解型EPS(S-EPS)、松散结合型EPS(LB-EPS)、疏水性S-EPS、疏水性LB-EPS的产生,降低了疏水性紧密结合型EPS(TB-EPS)的含量;从组成成分看,蛋白酶K促进了各类EPS腐殖质的生成,降低了疏水性蛋白的含量,S-EPS中β-折叠的相对含量减少是疏水性蛋白含量减少的主要原因.蛋白酶K的加入影响了微生物群落结构,相关性分析表明,起泡趋势和泡沫稳定性与疏水性TBEPS、疏水性多糖(PS)、疏水性蛋白质(PN)呈正相关,与LB-EPS呈负相关.Firmicutes门是与起泡特性参数最相关的门.蛋白酶K通过降低Firmicutes门中Syntrophomonas属、Fastidiosipila属的相对丰度,降低疏水性PS和疏水性PN的含量,增加LB-EPS的含量来达成其消泡能力.

Foaming,a common operational issue encountered in anaerobic digestion(AD) of food waste,has promoted the need for effective defoaming strategies.It is indicated that foaming occurs due to extracellular polymeric substances(EPS),particularly the hydrophobic protein components directly contributing to foam formation.In this study,different doses of proteinase K were added to food waste anaerobic digesters to investigate their impact on EPS production characteristics and defoaming potential.The results revealed that proteinase K posed no biological toxicity toward anaerobes.Moreover,the experimental group treated with 0.2 mg·g^(-1) TS proteinase K exhibited a 12.35%±3.36% higher methane yieldcompared with the control group.Additionally,proteinase K was found to effectively reduce both the foaming tendency and foam stability in the digesters,indicating its potential as a defoaming agent.The addition of proteinase K to the anaerobic digesters altered the production characteristics of EPS,resulting in increased levels of soluble EPS(S-EPS),loosely bound EPS(LB-EPS),hydrophobic S-EPS,and hydrophobic LB-EPS,and decreased levels of hydrophobic tightly bound EPS(TB-EPS).Regarding EPS composition,proteinase K facilitated the formation of humus and reduced the content of hydrophobic proteins(PN) by decreasing the relative content of β-sheet in S-EPS.Furthermore,the addition of proteinase K influenced the microbial community structure.Correlation analysis revealed that foaming tendency and foam stability exhibited a positive correlation with hydrophobic TB-EPS,hydrophobic polysaccharides(PS),and hydrophobic PN but featured a negative correlation with LB-EPS.Firmicutes,the most significant phylum,played a vital role in influencing foaming characteristic parameters.Proteinase K demonstrated its defoaming ability by reducing the relative abundance of genera Syntrophomonas and Fastidiosipila associated with the phylum Firmicutes.This decrease was accompanied by a reduction in the levels of hydrophobic PS and hydrophobic PN,along with an increase in the content of LB-EPS.