剩余污泥衰减系数取值范围探讨

Discussion on the Value Range of Excess Sludge Decay Coefficient

剩余污泥量是污水处理厂设计和运行的重要参数。我国《室外排水设计标准》(GB50014—2021)中给出了按污泥产率系数、衰减系数及不可生物降解和惰性悬浮物计算污水处理厂剩余污泥量的公式,但该公式中的污泥衰减系数(Kd)取值范围(0.04~0.075 d^(-1))不能适应进水中含有较高浓度不可生物降解悬浮物在长污泥龄下的情况。基于污泥龄的概念,通过理论推导给出了该计算公式中Kd的表达式,说明了Kd的实质含义和影响因素,指出Kd并不是一个常数,其值随污泥龄和不可生物降解悬浮物在反应池中的累积浓度占混合液挥发性悬浮固体浓度的比例不同而不同。可由污泥龄和进水中不可生物降解悬浮物浓度与可生物降解有机污染物浓度比值判断Kd的取值。所列举的工程实例的适宜Kd值为0.03 d-1。可为改进和拓宽该剩余污泥量计算公式的应用范围提供有益帮助。

The amount of excess sludge is an important factor in the design and operation of wastewater treatment plants. The formula for calculating the excess sludge quantity in wastewater treatment plants according to sludge yield coefficient, decay coefficient(Kd) and non-biodegradable and inert suspended solids is proposed in Standard for Design of Outdoor Wastewater Engineering(GB 50014-2021). However, the value range of sludge decay coefficient(0.04-0.075 d^(-1)) in this formula cannot adapt to the condition that the influent contains a high concentration of non-biodegradable suspended solids with a long sludge age. Based on the concept of sludge age, the paper introduced the expression of sludge decay coefficient by theoretical derivation, illustrated the essential meaning and influence factors of sludge decay coefficient, and pointed out that decay coefficient was not a constant and its value varied with sludge age and the proportion of non-biodegradable suspended solid cumulative concentration in the reaction tank to the concentration of volatile suspended solids in the mixed liquor. It is proposed that the value of Kdcan be judged by the sludge age and the ratio of the concentration of non-biodegradable suspended solids and the concentration of biodegradable organic pollutants in the influent. A Kdvalue of 0.03 d-1is appropriate for an engineering example cited in this paper. This research is expected to provide useful help for improving and broadening the application range of the formula.