Hybrid alkali-hydrodynamic disintegration of waste-activated sludge before two-stage anaerobic digestion process

Abstract

The first step of anaerobic digestion, the hydrolysis, is regarded as the rate-limiting step in the degradation of complex organic compounds, such as waste-activated sludge (WAS). The aim of lab-scale experiments was to pre-hydrolyze the sludge by means of low intensive alkaline sludge conditioning before applying hydrodynamic disintegration, as the pre-treatment procedure. Application of both processes as a hybrid disintegration sludge technology resulted in a higher organic matter release (soluble chemical oxygen demand (SCOD)) to the liquid sludge phase compared with the effects of processes conducted separately. The total SCOD after alkalization at 9 pH (pH in the range of 8.96–9.10, SCOD = 600 mg O2/L) and after hydrodynamic (SCOD = 1450 mg O2/L) disintegration equaled to 2050 mg/L. However, due to the synergistic effect, the obtained SCOD value amounted to 2800 mg/L, which constitutes an additional chemical oxygen demand (COD) dissolution of about 35 %. Similarly, the synergistic effect after alkalization at 10 pH was also obtained. The applied hybrid pre-hydrolysis technology resulted in a disintegration degree of 28–35 %. The experiments aimed at selection of the most appropriate procedures in terms of optimal sludge digestion results, including high organic matter degradation (removal) and high biogas production. The analyzed soft hybrid technology influenced the effectiveness of mesophilic/thermophilic anaerobic digestion in a positive way and ensured the sludge minimization. The adopted pre-treatment technology (alkalization + hydrodynamic cavitation) resulted in 22–27 % higher biogas production and 13–28 % higher biogas yield. After two stages of anaerobic digestion (mesophilic conditions (MAD) + thermophilic anaerobic digestion (TAD)), the highest total solids (TS) reduction amounted to 45.6 % and was received for the following sample at 7 days MAD + 17 days TAD. About 7 % higher TS reduction was noticed compared with the sample after 9 days MAD + 15 days TAD. Similar results were obtained for volatile solids (VS) reduction after two-stage anaerobic digestion. The highest decrease of VS was obtained when the first stage, the mesophilic digestion which lasted 7 days, was followed by thermophilic digestion for 17 days.

Is anaerobic digestion a reliable barrier for deactivation of pathogens in biosludge?

“…containing undetectable levels of pathogens, can be used for agricultural purposes. However, 75% of the stabilized sewage sludge used for agriculture belonged to Class B biosolids with pathogens (Grübel and Suschka, 2015). For Class A biosolids, of the level of fecal coliforms as an indicator of pathogen should be strictly monitored, while the monitoring of enteric viruses, helminth ova, and Salmonella spp.…”

Performance of thermophilic anaerobic sludge digester after alkaline‐assisted thermal disintegration optimization using response surface methodology

“…The Grübel & Suschka () reported that after two stages of anaerobic digestion (mesophilic and thermophilic anaerobic digestion), the highest TS reduction amounted to 45.6% (Grübel & Suschka ). Kavitha et al .…”

“…The Gr€ ubel & Suschka (2015) reported that after two stages of anaerobic digestion (mesophilic and thermophilic anaerobic digestion), the highest TS reduction amounted to 45.6% (Gr€ ubel & Suschka 2015). Kavitha et al (2016) investigated the effect of combined surfactant-dispersion pretreatment on dairy waste activated sludge) reduction in anaerobic digesters.…”

Disintegration of Wastewater Activated Sludge (WAS) for Improved Biogas Production: A Mini Review

“…In recent years, several pre-treatment / disintegration methods have been applied both on a bench and technical scale, for example by using thermal energy [23,24], enzymes [25], ozonisation [26], acidification [27], alkalization [28,29], high pressure [30,31], mechanical grinding [32] and ultrasound energy [33,34]. In general, these techniques can be split into 3 categories: biological, physical and chemical (Fig.…”