Enhancement of waste activated sludge (WAS) anaerobic digestion by means of pre- and intermediate treatments. Technical and economic analysis at a full-scale WWTP

JOURNAL OF ENVIRONMENTAL MANAGEMENT

卷:216

Article; Proceedings Paper

Campo, Giuseppe¹  Cerutti, Alberto¹  Zanetti, Mariachiara¹  Scibilia, Gerardo²  Lorenzi, Eugenio²  Ruffino, Barbara¹ 

[1] Politecn Torino, Dept Environm Land & Infrastruct Engn, Corso Duca Abruzzi 24, I-10129 Turin, Italy

[2] Soc Metropolitana Acque Torino SpA, Via Po 2, I-10090 Castiglione Torinese, TO, Italy

关键词: Waste activated sludge (WAS);    Cellular lysis;    Two-stage anaerobic digestion;    Intermediate hydrolysis treatment;    Cost-benefit assessment;   

DOI  :  10.1016/j.jenvman.2017.05.025

来源: Elsevier

【 摘 要 】

Anaerobic digestion (AD) is the most commonly applied end-treatment for the excess of waste activated sludge (WAS) generated in biological wastewater treatment processes. The efficacy of different typologies of pre-treatments in liberating intra-cellular organic substances and make them more usable for AD was demonstrated in several studies. However, the production of new extracellular polymeric substances (EPSs) that occur during an AD process, due to microbial metabolism, self-protective reactions and cell lysis, partially neutralizes the benefit of pre-treatments. The efficacy of post- and inter-stage treatments is currently under consideration to overcome the problems due to this unavoidable byproduct. This work compares three scenarios in which low-temperature (<100 degrees C) thermal and hybrid (thermal+alkali) lysis treatments were applied to one sample of WAS and two samples of digestate with hydraulic retention times (HRTs) of 7 and 15 days. Batch mesophilic digestibility tests demonstrated that intermediate treatments were effective in making the residual organic substance of a 7-day digestate usable for a second-stage AD process. In fact, under this scenario, the methane generated in a two-stage AD process, with an in-between intermediate treatment, was 23% and 16% higher than that generated in the scenario that considers traditional pre-treatments carried out with 4% NaOH at 70 and 90 degrees C respectively. Conversely, in no cases (70 or 90 degrees C) the combination of a 15-day AD process, followed by an intermediate treatment and a second-stage AD process, made possible to obtain specific methane productions (SMPs) higher than those obtained with pre-treatments. The results of the digestibility tests were used for a tecno-economic assessment of pre- and intermediate lysis treatments in a full scale wastewater treatment plant (WWTP, 2,000,000 p.e.). It was demonstrated that the introduction of thermal or hybrid pre-treatments could increase the revenues from the electricity sale by between 13% and 25%, in comparison with the present scenario (no lysis treatments). Conversely, intermediate treatments on a 7-day digestate could provide a gain of 26% or 32%, depending on the process temperature (70 or 90 degrees C). (C) 2017 Elsevier Ltd. All rights reserved.

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