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Abstract
With the annual increase in the sludge production in China’s sewage treatment plants, the problem of sewage sludge treatment and disposal is becoming more and more serious. Anaerobic fermentation can convert complex organic matter in sewage sludge into short-chain fatty acid, hydrogen, methane and other resources and is an effective method for sewage sludge treatment and disposal. At the same time, sewage sludge often contains flocculants, which will inevitably affect the effect of anaerobic fermentation. As a high-performance flocculant, polyaluminum chloride (PAC) is widely used in wastewater treatment and sewage sludge dewatering processes. Previous studies indicated that lower levels of PAC inhibit the effect of the anaerobic fermentation process of sewage sludge; on the other hand, it is necessary to understand the effects of higher levels of PAC in anaerobically fermented sewage sludge. The results showed that higher levels (0.2–1 g Al/g total solids (TS)) of PAC could promote acid production from anaerobically fermented sewage sludge. Moreover, mechanism studies suggest that higher levels (0.2–1 g Al/g total solids (TS)) of PAC caused excessive adsorption of the charge on the surface of the sewage sludge colloid and reversed the charge. The sewage sludge colloid was stabilized again, which increases the concentration of soluble proteins, polysaccharides, and soluble extracellular polymers (S-EPS) in the fermentation broth, thereby improving the anaerobically fermented sewage sludge efficiency. The results provided from this study may act as technical reference and guidance for the engineering application of sewage sludge anaerobic fermentation.
Highlights
Biological wastewater treatment is widely used in the world because it is considered as an effective and inexpensive pollution treatment [1,2], but a significant amount of sewage sludge is produced during this process
Chen et al [15] studied the effect of polyaluminum chloride on anaerobically fermented sewage sludge, and the results showed that the presence of 30 mg Al/g total solids (TS) of PAC in sewage sludge significantly reduces the production of short-chain fatty acids in sewage sludge anaerobic fermentation compared with the control group
It can be seen that as the PAC increases from 0–0.15 g Al/g TS, the maximum short-chain fatty acids (SCFAs) yield is reduced from 1190 mg/L to 659 mg/L
Summary
Biological wastewater treatment is widely used in the world because it is considered as an effective and inexpensive pollution treatment [1,2], but a significant amount of sewage sludge is produced during this process. It is estimated that the European Union annually produces more than 50 million tons of sewage sludge (calculated based on 80% moisture content) [3], while China produced 35 million tons of sewage sludge 80% moisture content) in 2015, and this number is expected to trend upward [4]. More and more sewage sludge poses challenges and opportunities. The challenge lies in the complex composition of sewage sludge, which contains many pollutants, including pathogens, parasites, heavy metal elements, etc. Opportunity lies in the sewage sludge as it contains a large amount of biodegradable If improperly handled and disposed of, it will pollute the environment and even endanger the safety of surrounding residents [5].
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