In this study, the organic loading rate (OLR) of a high-solids anaerobic digestion (HSAD) system was increased from 3.4 to 5.0 gVS L^–1 day^–1 and reactor stability, performance and microbial community structure were determined. Laboratory simulations (3.5 L) of the full-scale process (500 dry ton year^–1) were conducted using continuously stirred-tank mesophilic reactors. OLRs of 3.4 gVS L^–1day^–1 (equal to the full-scale HSAD), 4.0, 4.5 and 5.0 gVS L^–1day^–1 were evaluated. Biochemical parameters and archaeal community dynamics were measured over 42 days of steady state operation. Results showed that increasing OLR increased the amount of organic matter conversion and resulted in higher organic matter removal and volumetric methane (CH₄) production (VMP) rates. The highest volatile solids (VS) removal and VMP results of 54 ± 2% and 1.4 ± 0.1 L CH₄ L^–1day^–1 were observed for 5.0 gVS L^–1 day^–1. The efficiency of reactor conversion of organic matter to CH₄ was found to be similar in all the treatments with an average value of 0.57 ± 0.07 LCH₄ gVS^–1 _removed. 16S rRNA gene terminal restriction fragment polymorphism (T-RFLP) analyses revealed that archaeal TRFs remained stable during the experiment accounting for an average relative abundance (RA) of 81 ± 1%. Archaea consistent with multiple terminal restriction fragments (TRFs) included members of the Euryarchaeota and Crenarchaeota phyla, including acetoclastic and hydrogenotrophic groups. In conclusion, this laboratory-scale study suggests that performance and stability as well as the archaeal community structure in this HSAD system was unaffected by increasing the OLR by nearly 50% and that this increase resulted in a similar increase in the amount of CH₄ gas generated.

The objective of the present study was to study the effect of two vermicomposts [animal (VCD) and vegetal origin (VGF)] and a cotton gin compost (C) at rates of 1780 and 3560 kg fresh organic matter ha^–1 for 3 years on an Typic Xerofluvent located near Seville (Spain) on soil biological properties, nutrition (leaf N, P and K concentration, pigments and soluble carbohydrate concentrations) and yield parameters of maize (Zea mays cv. Tundra) crop. All organic waste materials had a positive effect on the soil biological properties, plant nutrition and crop yield parameters, although at the end of the experimental period and at the high organic matter rate, the soil microbial biomass and dehydrogenase, urease, β-glucosidase, phosphatase and arylsulfatase activities increased more significantly in the VCD-amended soils (86.4, 85.8, 94.5, 99.3, 70.1 and 63.8%, respectively) respect to the control soil, followed by VGF-amended soils (84.8, 80.6, 92.7, 99.1, 68.3 and 61.6%, respectively) and CC-amended soils (80.5, 75.9, 89.7, 99, 65.7 and 59.9%, respectively). Leaf N, P and K contents and pigments and soluble carbohydrate contents were highest in VCD-amended soils, followed by VGF and CC treatments. Compared with the control soil, the application of VCD in soils at high doses increased the crop yield parameters, followed by VGF and CC treatments. This may have been due to a greater labile fraction of organic matter in the VCD than the VGF and CC, respectively.

Using the solid waste management programmes of three barangays (the smallest unit of local government in the Philippines) in Quezon City, Metro Manila, as a case study, this research aimed to further the development of efficient organic waste recycling systems through the promotion of urban agricultural activities on green and vacant spaces. First, the quantity of organic waste and compost produced through ongoing barangay projects was measured. The amount of compost that could potentially be utilized on farmland and vacant land within the barangays was then identified to determine the possibility of a local recycling system. The results indicate that, at present, securing buyers for compost is difficult and, therefore, most compost is distributed to large neighbouring farm villages. However, the present analysis of potential compost use within the barangay demonstrates that a more local compost recycling system is indeed feasible.