Vermi-Conversion of Anaerobic Sludges by <i>Eisenia fetida</i> Earthworms

Sludge management is considered a difficult and challenging task and is a priority of environmental policy. This study evaluates the transformation of the anaerobic sludge of agroindustrial wastes (cow manure, anaerobic sludge mixtures) directly to compost using Eisenia fetida earthworms (vermicomposting) in relation to sludge quality; moreover, it investigates the effects of different sludge compositions on vermicompost physicochemical properties. In particular, the biostabilization of anaerobic sludge (AS1) produced in excess from the wastewater treatment plant (WWTP) of Patras, Greece, and mixed anaerobic sludge (AS2) originating from the effluents of a laboratory anaerobic co-digestion system treating an agroindustrial waste mixture (olive mill wastewater, cheese whey, and liquid cow manure in a ratio of 55: 40: 5 (w/w), respectively) mixed with cow dung (CD) using Eisenia fetida earthworms was examined. Comparing the mixtures of CD-AS1 to CD-AS2, superior results were obtained with the use of AS2 since an increase in N-P-K was observed when either 10% (22%, 51.8%, and 2.4%, respectively) or 15% of AS2 (38.7%, 14.1%, and 8.1% respectively) was used. Although a reduction in earthworms’ growth was observed compared to 100% CD, during the vermicomposting of the CD-AS mixtures, 410 and 250 mg/earthworm was sustained in the mixtures of 85% CD-15% AS2 and 80% CD-20% AS2 after a period of 63 and 70 days of vermicomposting, respectively

Assessment of Single- vs. Two-Stage Process for the Anaerobic Digestion of Liquid Cow Manure and Cheese Whey

The growing interest in processes that involve biomass conversion to renewable energy, such as anaerobic digestion, has stimulated research in this field in order to assess the optimum conditions for biogas production from abundant feedstocks, like agro-industrial wastes. Anaerobic digestion is an attractive process for the decomposition of organic wastes via a complex microbial consortium and subsequent conversion of metabolic intermediates to hydrogen and methane. The present study focused on the exploitation of liquid cow manure (LCM) and cheese whey (CW) as noneasily and easily biodegradable sources, respectively, using continuous stirred-tank reactors for biogas production, and a comparison was presented between single- and two-stage anaerobic digestion systems. No significant differences were found concerning LCM treatment, in a two-stage system compared to a single one, concluding that LCM can be treated by implementing a single-stage process, as a recalcitrant substrate, with the greatest methane production rate of 0.67 L CH4/(LR·d) at an HRT of 16 d. On the other hand, using the easily biodegradable CW as a monosubstrate, the two-stage process was considered a better treatment system compared to a single one. During the single-stage process, operational problems were observed due to the limited buffering capacity of CW. However, the two-stage anaerobic digestion of CW produced a stable methane production rate of 0.68 L CH4/(LR·d) or 13.7 L CH4/Lfeed, while the total COD was removed by 76%