Abstract
Drinking water treatment sludge (DWTS) is a waste by-product from water treatment plants where aluminum and iron salts are the most commonly used coagulants. DWTS was reused to investigate the effects of DWTS on the digestion liquid quality and microorganism activity of excess activated sludge (EAS). DWTS with four suspended solid (SS) concentrations (0%, 2%, 5% and 10%) was added to EAS which was sampled during aerobic and anaerobic digestion processes, then batch tests were carried out which followed the coagulation-flocculation process. It was found that DWTS can improve total dissolved nitrogen (TDN) and dissolved phosphorus (DP) removal efficiencies for anaerobic EAS. The highest removal efficiency of TDN (29.97%) as well as DP (55.38%) was observed when DWTS dosage was SS = 10%. The release of dissolved organic matter (DOM) by DWTS could increase dissolved organic carbon (DOC) concentration and lead to the accumulation of non-biodegradable humic acid-like substance in aerobic and anaerobic digestion liquid. The dehydrogenase activity (DHA) values of anaerobic EAS were higher than aerobic EAS. DWTS could reduce DHA for both EAS. These results indicate that potential risk of release of DOM should be considered when reusing DWTS in future research.
Highlights
The number of municipal wastewater treatment plants (MWTPs) increased sharply, resulting in the generation of large volumes of excess activated sludge (EAS)
During the process of aerobic and anaerobic digestion, the degradation of nitrogenous matter can lead to the production of high concentration of ammonium nitrogen, which affects the activity of microorganisms [3,6,7]
It has been observed that humic acids contained in EAS could limit the conversion of organic compounds into energy [10,11]
Summary
The number of municipal wastewater treatment plants (MWTPs) increased sharply, resulting in the generation of large volumes of excess activated sludge (EAS). On the other hand, drinking water treatment sludge (DWTS) is a waste by-product from the drinking water treatment process, which contains high content of aluminum or iron species due to the use of different types of coagulants [12]. From the perspective of sustainable development, the recovery and utilization of DWTS has been investigated in different fields (e.g., building material, support material for the manufacture of compost, adsorbent for phosphorus removal, and coagulant for treating wastewater) and is considered as an effective approach for reducing waste disposal [14,15,16,17]. There are few studies on recycling DWTS to treat EAS during aerobic and anaerobic digestion processes. In order to determine the effects of DWTS on the EAS aerobic and anaerobic digestion processes, the changes of supernatant and sludge were comprehensively considered. The main issues considered in this paper are: (1) evaluation of the effect of DWTS on the removal of nitrogen and phosphorus in digestion liquid, (2) assessment of the effect of DWTS on DOM produced in the digestion of EAS, and (3) possible mechanism analysis of the impact of DWTS on the dehydrogenase activity (DHA) of EAS
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