Effects of coal ash supplementation on aerobic granular sludge cultivated in a simultaneous fill/draw sequencing batch reactor

ABSTRACT This study aimed to verify if coal ash, a residue from thermal power plants, could act as a granulation nucleus, cations source, and abrasive element to favor granules formation and stability in aerobic granular sludge (AGS) systems. Two simultaneous fill/draw sequencing batch reactors (SBRs) (R1 and R2) were operated with 6-h cycles, i.e., the filling and drawing phases occurred simultaneously, followed by the reaction and settling phases. R1 was maintained as control, while R2 was supplemented with coal ash (1 g·L-1) on the first day of operation. Granulation was achieved in both reactors, and no significant differences were observed in terms of settleability, biomass retention, morphology, resistance to shear, and composition of the EPS matrix. However, the ash addition did not change the settleability, biomass retention, granule morphology, shear resistance, and extracellular polymeric substances (EPS) content significantly. COD removal was high (≥ 90%), while nitrogen (~50%) and phosphorus (~40%) removals were low, possibly due to the presence of nitrate during the anaerobic phase. With granulation, microbial population profile was altered, mainly at the genus level. In general, the operational conditions had a more considerable influence over granulation than the ash addition. The possible reasons are because the ash supplementation was performed in a single step, the low sedimentation rate of this particular residue, and the weak interaction between the ash and the EPS formed in the granular sludge. These factors appear to have decreased or prevented the action of the ash as granulation nucleus, source of cations, and abrasive element.

摘要 本研究旨在验证火力发电厂产生的残渣——粉煤灰，是否可作为造粒核心、阳离子源与磨蚀性组分，以促进好氧颗粒污泥（aerobic granular sludge, AGS）系统中颗粒的形成与稳定性。本研究设置两台同步进水/排水的序批式反应器（sequencing batch reactors, SBRs，编号为R1与R2），运行周期为6小时，即进水与排水阶段同步进行，随后依次开展反应与沉降阶段。R1作为对照组维持常规运行，R2则在运行首日投加1 g·L⁻¹的粉煤灰。两台反应器均成功实现颗粒化，二者在沉降性能、生物质留存量、形态特征、抗剪切能力及胞外聚合物（extracellular polymeric substances, EPS）基质组成方面均未观察到显著差异。不过，粉煤灰投加并未显著改变沉降性能、生物质留存量、颗粒形态、抗剪切能力及EPS含量。化学需氧量（Chemical Oxygen Demand, COD）去除率较高（≥90%），而氮（约50%）与磷（约40%）的去除率较低，这可能与厌氧阶段存在硝酸盐有关。随着颗粒化过程的推进，微生物群落结构发生改变，尤其在属水平上表现更为明显。总体而言，运行条件对颗粒化的影响远大于粉煤灰投加。其潜在原因可能包括：粉煤灰采用一次性投加方式、该类残渣自身沉降速率较低，以及粉煤灰与颗粒污泥中形成的EPS之间相互作用较弱。上述因素似乎削弱甚至阻碍了粉煤灰作为造粒核心、阳离子源与磨蚀性组分的作用。