Stimulating effect of hydrostatic pressure on ultrasonic sewage sludge treatment for COD solubilization and methane production.

The performance of ultrasonic treatment was assessed under different hydrostatic pressures for two different waste activated sludges. The impact of pressurized sonication was evaluated based on the degree of disintegration (DDCOD) and the specific methane yield (SMY). An enhancement of DDCOD was observed at an intermediate pressure level (max. 53% at 1.0 bar), but at higher pressure levels (up to 3.5 bar), the enhancement was not as pronounced as for the intermediate ranges (max. 11%). In contrast to DDCOD, SMY increased with increasing pressure for both sludge samples tested (max 17% at 3.5 bar) so that SMY did not show a notable correlation with DDCOD. A positive energy balance (max. 167%) considering the energy input for ultrasonication and the additional methane generated was only achieved in samples treated under elevated hydrostatic pressure. Since this can be achieved with negligible effort, the enhancement can be considered as "methane for free".

A new approach to enhance the conventional two-phase anaerobic co-digestion of food waste and sewage sludge.

BACKGROUND: Two-phase anaerobic co-digestion (TAcoD) is a versatile technology for the simultaneous treatment of organic materials and biogas production. However, the produced digestate and supernatant of the system contain heavy metals and organic substances that need to be treated prior to discharge or land application. Therefore, in this study, an innovative TAcoD for organic fertilizer and high supernatant quality achievement was proposed. METHODS: In the conventional TAcoD, mixed sewage sludge (SS) and food waste (FW) were first hydrolyzed in the acidogenic reactor, and then the hydrolyzate substrate was subjected to the methanogenic reactor (TAcoD 1). In the modified TAcoD (TAcoD 2), only FW was fed into the acidogenic reactor, and the produced hydrolyzed solid was directly converted to the organic fertilizer, while the supernatant with high soluble chemical demand (SCOD) concentration was further co-digested with SS in the methanogenic reactor. RESULTS: Although TAcoD 1 produced bio-methane yield and potential energy of 56.18% and 1.6-fold higher than TAcoD 2, the economical valorization of TAcoD 2 was 9-fold of that from TAcoD 1. The supernatant quality of TAcoD 2 was far better than TAcoD 1, since the SCOD, total nitrogen (TN), and total phosphor (TP) removal in TAcoD 2 and TAcoD 1 were 94.3%, 79.4%, 90.7%, and 68.9%, 28%, 46%, respectively. In terms of solid waste management, the modified TAcoD converted FW to organic fertilizer and achieved a solid reduction of 43.62% higher than that of conventional TAcoD. CONCLUSIONS: This new modification in two-phase anaerobic co-digestion of food waste and sewage sludge provides a potentially feasible practice for simultaneous bio-methane, organic fertilizer, and high supernatant quality achievement. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40201-020-00603-8.

Impacts of different operational temperatures and organic loads in anaerobic co-digestion of food waste and sewage sludge on the fate of SARS-CoV-2.

The impacts of different operational temperatures, and organic load (OL) on the fate of SARS-CoV-2 during the anaerobic co-digestion of food waste (FW) and sewage sludge (SS) was evaluated. The lab-scaled batch reactors (i.e. R1-R7) were performed under psychrophilic, mesophilic, and thermophilic conditions and the OL of systems was 1.5, 3.5, 6 gVS/L. The performance parameters showed that at higher OL the stability of systems failed and low biogas was produced. In contrast, increasing of operational temperature of systems induced more biogas generation due to the increment of metabolic activity of bacteria. Therefore, R1-R7 achieved biogas yield of 202.5, 249, 187, 260, 246, 163, and 300 mL/gVS respectively. Both SARS-CoV-2 genes i.e. ORF1ab, and N genes were detected in the effluent of psychrophilic reactors i.e. R1, and R2, with a total concentration of 46 × 103, and 11 × 103 copies/L respectively. In R3, no viral genes were observed, when the VFAs was accumulated up to 2000 mg/L and caused a pH drop to 5.6. At the mesophilic condition, the viral concentration was significantly declined, and no viral genes were observed at an OL of 3.5 gVS/L. Furthermore, the synergistic effect of temperature and accumulation of intermediate metabolites provided a sever condition for SARS-CoV-2 survival at an operational temperature and OL of 50 °C, and 1.5 gVS/L respectively.

Synergistic effects of co-trace elements on anaerobic co-digestion of food waste and sewage sludge at high organic load.

Trace elements play an indispensable role in stabilizing the performance of anaerobic co-digestion (Co-AD) of food waste (FW) and sewage sludge (SS) at greater organic load (OL). The results of high organic-loaded reactors showed that the stability of the system failed due to the buildup of volatile fatty acid (VFA) and ammonia. At the OL of 6.5 g/L, the stability of the system failed due to the buildup of propionic acid. The optimum dosage of Fe (5000 mg/L), Ni (200 mg/L), Zn (320 mg/L), and Mo (2.2 mg/L) was experimentally determined and added to reduce the inhibition condition. Consequently, the propionic acid concentration, which was above 1500 mg/L reduced to under 500 mg/L during Co-AD. Hence, higher biogas production, and biodegradability of 236 ± 23 mL/g VS, and 41.75%, respectively, were obtained. Increasing OL (9.5 g/L), the stability of the system was hindered due to only the buildup of ammonia (up to 188 ± 6 NH3-N mg/L). Therefore, the trace elements of Cu (250 mg/L) and Co (3 mg/L) were experimentally determined and added into the Co-AD to diminish ammonia accumulation and process instability. The experimental results showed that at OL of 14 g/L, biogas production, low ammonia concentration and biodegradability of 332 ± 21 mL/g VS, and 70 NH3-N mg/L, and 57.89%, respectively, were achieved. However, the performance and stability of the system failed at the higher OL due to the more increased ammonia and VFA concentration, and the greater dosages of trace elements did not enhance the process stability.