Comprehensive management of dog faeces: Composting versus anaerobic digestion

Abstract

The objective of this work was to study the possibilities to manage and recycle dog faeces (DF) using biological processes, using two approaches: composting (C) and anaerobic digestion (AD). Thus, different experiments have been carried out: i) two laboratory/pilot scale experiments (selfheating and composting tests) and one, on a commercial scale; ii) two AD experiments. In both approaches, municipal waste such as the organic fraction of municipal solid waste (OMSW) and urban pruning waste (GW) were used as co-substrates. The results obtained regarding the optimization of the composting process indicated that the best strategy was the use of a 1:2 ratio of DF, a 1:4 ratio of OMSW, and a 1:4 ratio of GW, according to the thermal parameters studied (temperature and cumulative quadratic exothermic index (EXI 2 )), and the quality of the compost obtained. A potentially limiting factor of the process was the high salinity of the DF waste. In addition, AD experiments were performed on DF, OMSW, and GW wastes in controlled anaerobic systems at a laboratory scale. In these experiments, the biogas production obtained was 229 mL biogas/g total solids for the DF residue, 248 mL biogas/g total solids for GW, and 263 mL biogas/g total solids for OMSW. The co-digestion yields a clear improvement in the efficiency of the process against the use of a single residue, increasing the production of biogas by up to 27% with respect to that of the DF waste alone during the first 25 days of AD. The results obtained with these procedures have shown the possibilities to add value to this waste in an urban context where the circular economy represents an increasingly favourable scenario, including the generation of fertilisers and/or energy at a local scale, provided that the collection of dog faeces is optimized.

Dog Waste in Biogas Production

“…In biodigesters B3 and B4, higher volumes of biogas were observed, compared to biodigesters B1 and B2. This was already expected, as dog waste has an excess of total nitrogen (NT) in relation to total organic carbon, so that aerobic or anaerobic self-degradation will not occur autonomously and it is necessary to mix it with other residues rich in carbon (MARTÍNEZ-SABATER et al, 2019).…”

“…The increase in the number of pets also contributes to the increase in waste generation. For example, a single dog can produce an average of 140 g to 340 g of waste per day, depending on the size of the animal (MARTÍNEZ-SABATER et al, 2019).…”

“…In comparison, fresh cattle manure contains 40% more nitrogen, the same amount of P2O5 and 1/20th the amount of K2O. Dog waste has an excess of total nitrogen (NT) in relation to total organic carbon so that aerobic or anaerobic self-degradation will not occur autonomously and it is necessary to mix it with other waste rich in carbon (MARTÍNEZ-SABATER et al, 2019). The food the dog consumes has a strong influence on the characteristics of the feces it produces.…”

Biodigestion System Made of Polyethylene and Polystyrene Insulator for Dog Farm (on the Example of the Republic of Chile)

“…As a second option for raw materials that provide a high C/N ratio, one could add the remains of vegetables such as wheat and corn cereal straw, including grass, cut grass, and dry leaves (which, in addition, all have a low lignin content) [105] or sheep, goat, or bovine feces, which have an inoculum rich in methanogenic bacteria that will guarantee the production of biogas [112]. Likewise, according to the theoretical comparison with bovine manure, the mixture of canine waste with vegetable biomass generates levels of biogas similar to that of bovines [113]; researchers have even identified potential vegetables that could be used to produce biodiesel that may enable co-digestion with bovine dung, generating a relevant increase in biogas production, such as Jatropha, a de-oiled cake [114], and others waste products with their oils extracted which can used for biodiesel and for biogas [115]. However, there are combinations that can decrease the anerobic process and generate less biogas, such as the addition of chicken manure, which contains high levels of ammonium, causing an imbalance in the digestion steps and thus leading to the potential accumulation of volatile fatty acids [98].…”

One Health approach to companion carnivores with special regard to raw-feeding

“…Therefore, it requires processing before it can be used to fertilise the soil. Martínez-Sabater et al (2019), mentioned the possibility of utilising biological processes such as composting and anaerobic digestion to add value to these wastes. However, these practices are neglected, especially in urban areas (Okoroigwe et al, 2014).…”