This work proved an efficient method to significantly increase methane production from anaerobic digestion of WAS. This method is to reflux proper of digestion liquid into waste activated sludge pretreatment unit (pH 9.5 for 24 h). The yield of maximum methane improved between 174.2 ± 7.3 and 282.5 ± 14.1 mL/g VSS with the reflux ratio of digestion liquid increasing from 0% to 20%. It was observed that the biodegradable organics in the digestion liquid did not affect the biological processes related to anaerobic digestion but increased methane production through reutilization. The ammonium in the digestion liquid was the main contributor to the increase in methane production via promoting sludge solubilization, but refractory organics were the major inhibitors to anaerobic digestion. It should be emphasized that the metal ions present in the digestion liquid were beneficial rather than harmful to the biological processes in the anaerobic digestion, which may be connected with the fact that certain metal ions were involved in the expression and activation of key enzymes. In addition, it was found that anaerobes in digestion liquid were another potential contributor to the enhanced anaerobic digestion.

这项工作证明了有效提高WAS厌氧消化甲烷产量的有效方法。该方法是将消化液适当回流到废活性污泥预处理单元（pH 9.5，持续24 h）中。当消化液的回流比从0％增加到20％时，最大甲烷产率在174.2±7.3和282.5±14.1 mL / g VSS之间提高。观察到消化液中可生物降解的有机物不会影响与厌氧消化有关的生物过程，但会通过再利用增加甲烷产量。消化液中的铵是通过促进污泥溶解而增加甲烷产量的主要因素，但是难熔有机物是厌氧消化的主要抑制剂。应该强调的是，存在于消化液中的金属离子对厌氧消化中的生物过程是有益的，而不是有害的，这可能与某些金属离子参与关键酶的表达和活化有关。另外，发现消化液中的厌氧菌是增强厌氧消化的另一个潜在因素。