Abstract
The effect of adding alum water treatment residues (WTR) on the methanogenic activity in the digestion of primary domestic wastewater sludge was evaluated through laboratory experiments in sedimentation columns, using total suspended solids (TSS) concentrations from 0.37 to 1.23 g/L. The addition of WTR to primary clarifiers can benefit its effluent water quality in terms of colour, turbidity, chemical oxygen demand (COD), and TSS. However, the presence of WTR can negatively influence the production of methane gas during organic sludge digestion in primary clarifiers, for concentrations of TSS between 14.43 and 25.23 g/L and of VSS between 10.2 and 11.85 g/L. The activity of the Methanothrix sp., curved bacilli, methanococci, and Methanosarcina sp. decreases considerably after 16 days of anaerobic digestion, and methane production seems to only be associated with fluorescent methanogenic bacilli.
Highlights
The production of drinking water in water treatment plants (WTP) involves the removal of several suspended and dissolved compounds, such as inorganic compounds and organic compounds, consisting of humic substances which change the colour and turbidity of water, such as planktonic organisms, bacteria, protozoa, and viruses
For the water treatment residues (WTR), between 78.3% and 80.2% of total suspended solids (TSS) is composed of fixed solids, i.e., most of the solid material is formed by inorganic substances, being compatible with the values found by [22,31], which describes most of the solid’s content in the WTR as inert
21.7%, which is contrary to that observed in the Domestic wastewater (DWW) samples, where 85.4% of the TSS is of the volatile type, due to the presence of organic matter
Summary
The production of drinking water in water treatment plants (WTP) involves the removal of several suspended and dissolved compounds, such as inorganic compounds (e.g., clay, silt, and sand) and organic compounds, consisting of humic substances which change the colour and turbidity of water, such as planktonic organisms, bacteria, protozoa, and viruses. In order to remove inorganic and organic compounds from water, several reagents can be used, such as coagulants, which destabilise the organic particles leading to the formation of precipitates called water treatment sludge or water treatment residues (WTR) [1]. These residues are essentially accumulated in the decanters and filters of the WTP, varying in their volume between 0.1% and 1.5% of the total volume of the treated water [2,3]. Brazilian Law No 12.305/2010 [5]
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