Sludge bulking caused by the overgrowth of filamentous bacteria, especially Microthrix parvicella, has been observed in WWTPs worldwide during low-temperature periods. In this study, the impacts of sludge load on the in situ growth of M. parvicella and sludge settleability were first evaluated at 15 °C over a period of 500 d using a bench-scale anaerobic-anoxic-aerobic reactor fed with raw sewage from a full-scale WWTP. When the reactor was operated at a sludge load of 0.07 ± 0.015 kg COD (kg MLSS·d)⁻¹ for 120 d, the sludge volume index (SVI) increased gradually from 85 mL g⁻¹ to 157 mL g⁻¹, and the abundance of M. parvicella quantified by qPCR and FISH methods also increased from 0.42% to 4.63% and 1.56%–13.59%, respectively. When the sludge load was further reduced to 0.04 ± 0.004 kg COD (kg MLSS·d)⁻¹, the SVI value varied in a narrow range of 135–164 mL g⁻¹ over a duration of 280 d, while the M. parvicella abundance increased to the maximum values of 10.13% (qPCR) and 18.53% (FISH), respectively. When the sludge load was increased to 0.12 ± 0.016 kg COD (kg MLSS·d)⁻¹, filamentous abundance and SVI were reduced to 1.06% (qPCR) and 105 mL g⁻¹ within 100 d, suggesting that it might be possible to control the growth of M. parvicella by keeping the sludge load above 0.1 kg COD (kg MLSS·d)⁻¹. The feasibility of the strategy was further validated in the same WWTP. It was found that the SVI and filamentous abundance in winter were successfully controlled for two successive years at below 120 mL g⁻¹ and 7% (FISH), respectively, when the sludge load was maintained at 0.14 ± 0.04 kg COD (kg MLSS·d)⁻¹ by adjusting sludge discharge, proving that this sludge-load-based strategy could be an efficient approach to control filamentous bulking.

在全球范围内的低温污水处理厂中，已观察到丝状细菌（尤其是Microthrix parvicella）的过度生长引起的污泥膨胀。在这项研究中，污泥负荷对影响原位生长M. parvicella和污泥沉降首先在15℃使用与来自未经处理的污水送入工作台规模厌氧-无氧-好氧反应器在某一时期500 d的全面的污水处理厂。当反应器在0.07±0.015 kg COD（kg MLSS·d）^-1的污泥负荷下运行120 d时，污泥体积指数（SVI）从85 mL g ^-1逐渐增加到157 mL g ^-1，并且帕尔维切菌的丰度通过qPCR和FISH方法定量的结果也分别从0.42％增加到4.63％和1.56％–13.59％。当污泥负荷进一步降低到0.04±0.004公斤COD（公斤·MLSS ^d）-1，在一个窄的范围135-164毫升克而变化的SVI值^-1 280 d的持续时间，而M. parvicella丰度分别增加到最大值10.13％（qPCR）和18.53％（FISH）。当污泥负荷增加到0.12±0.016 kg COD（kg MLSS·d）^-1时，丝状丰度和SVI在100 d内降低到1.06％（qPCR）和105 mL g ^-1，这表明可能通过将污泥负荷保持在0.1 kg COD（kg MLSS·d）^-1以上来控制小枝分枝杆菌的生长。该策略的可行性在同一污水处理厂得到了进一步验证。据发现，所述SVI和丝状丰度在冬季成功控制连续两年在低于120毫升克^-1和7％（FISH），分别，当污泥负荷保持在0.14±0.04公斤COD（公斤·MLSS d）^-1通过调整污泥排放量，证明基于污泥负荷的策略可能是控制丝状堆积的有效方法。