Abstract
In Chile, small wastewater treatment plants (WWTPs) (treatment capacity of less than 4,800 m3/d) are normally not designed with consideration for the potential valorization of generated sludge. For this reason, they are generally operated at high solids residence times (SRT) (15 d) to promote the decay of biomass, promoting less sludge production and reducing the costs associated with biomass management. Operation at high SRT implies the need for a larger activated sludge system, increasing capital costs. The implementation of a sludge-disintegration unit by ozonation in future WWTPs could enable operation at an SRT of 3 d, with low sludge generation. In this work, we evaluate how the implementation of a sludge-ozonation system in small WWTPs (200–4000 m3/d) would affect treatment costs. Four scenarios were studied: (1) a current WWTP operated at an SRT of 15 d, without a sludge ozonation system; (2) a WWTP operated at an SRT of 15 d, with a sludge-ozonation system that would achieve zero sludge production; (3) a WWTP operated at an SRT of 3 d, with a sludge-ozonation system that would provide the same sludge production as scenario 1; (4) a WWTP operated at an SRT of 15 d, with a sludge-ozonation system that would achieve zero sludge production. Economic analysis shows that the treatment costs for scenarios 1 and 2 are similar, while a reduction in cost of up to 47% is obtained for scenarios 3 and 4.
Highlights
The management of sewage sludge is an important issue for wastewater treatment systems
In WWTPs where a sludge-ozonation system is implemented, the reduction in sludge generation and the increase energy consumption depend on the specific ozone dose supplied and on the daily fraction of sludge ozonated, as well as the solids residence times (SRT) applied in the activated sludge reactor
For a fixed daily specific ozone dose, the reduction in sludge generation and the increase in energy consumption is less with an increased SRT
Summary
The management of sewage sludge is an important issue for wastewater treatment systems. Of their influent flow, sludge management represents around 50–60% of the total operating costs of WWTPs [1,2] To address this in a more sustainable manner, sewage-sludge management has evolved from an approach involving only treatment and disposal to one considering conversion into value-added products (i.e., bioenergy or biobased materials). The latter alternative has the potential to reduce the quantity of sludge that needs to be disposed of and can reduce overall operating costs [3,4].
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