Decentralized composting has been proposed as a best available practice, with a highly positive impact on municipal solid wastes management plans. However, in cold climates, decentralized small-scale composting performance to reach thermophilic temperatures (required for the product sanitization) could be poor, due to a lack of critical mass to retain heat. In addition, in these systems the composting process is usually disturbed when new portions of fresh organic waste are combined with previous batches. This causes modifications in the well-known composting evolution pattern. The objective of this work was to improve the understanding of these technical aspects through a real-scale decentralized composting experience carried out under cold climate conditions, in order to assess sanitization performance and to study the effects of fresh feedstock additions in the process evolution. Kitchen and garden organic wastes were composted in 500 L-static compost bins (without turning) for 244 days under cold climate conditions (Bariloche, NW Patagonia, Argentina), using pine wood shavings in a ratio of 1.5:1 v: v (waste: bulking agent). Temperature profile, stability indicators (microbial activity, carbon and nitrogen contents and ratio) and other variables (pH and electrical conductivity), were monitored throughout the experience. Our results indicate that small-scale composting (average generation rate of 7 kg d) is viable under cold weather conditions, since thermophilic sanitization temperatures (> 55 °C) were maintained for 3 consecutive days in most of the composting mass, according to available USEPA regulations commonly used as a reference for pathogens control in sewage sludge. On the other hand, stability indicators showed a differentiated organic matter degradation process along the compost bins height. Particularly, in the bottommost composting mix layer the process took a longer period to achieve compost stability than the upper layers, suggesting that differential organic matter transformation appears not to be necessarily associated to the order of the waste batches incorporation in a time line, as it could be expected. These findings suggest the need to discuss new ways of studying the composting process in small-scale compost bins as well as their commercial design.

Oil-based drilling cuttings comprise a large and hazardous waste stream generated by oil and gas wells drilling operations. Oil-based cuttings are muddy materials with high contents of salts and hydrocarbons. Composting strategies have shown to be effective in the biodegradation of petroleum hydrocarbons, and it offers numerous advantages in comparison with other bioremediation methods. In order to assess the effectiveness of drilling cuttings bioremediation by composting with food and garden wastes, an experiment was conducted in 60-L reactors for 151 days. Four treatments were carried out: only oil-based cuttings, two proportions (in a volume basis) of organic wastes to drilling cuttings (33 and 75 %) and only organic wastes (as a traditional composting reference), with pine-tree woodchips as bulking agent. High degradation percentages of total hydrocarbons (&82 %), n-alkanes (&96 %) and the 16 USEPA-listed polycyclic aromatic hydrocarbons (&93 %) were reached in the treatment with 75 % of organic wastes, and applying 33 % of organic wastes was not more effective than not applying organic wastes for the drilling cuttings hydrocarbons biodegradation. Furthermore, in the treatment with 75 % of organic wastes, alkanes half-life and polycyclic aromatic hydrocarbons half-life were about 10 times and four times lower, respectively, than those in the treatment with 33 % of organic wastes. Possibly, lower hydrocarbons and salts initial concentrations (i.e., lower toxicity), higher microbial counts, adequate nutrient proportions and water content supported a high biological activity with a consequent elevated biodegradation rate in the treatment with 75 % of organic wastes.

Abstract-Decentralized composting has become a powerful option for municipal organic waste management. This technology, not only is an effective tool to treat organic waste, producing compost as a valuable by-product, but also represents an innovative way to involve waste generators in treatment operations. Decentralized composting contributes to reducing waste transportation, treatment costs and landfilling volumes thus resulting in a positive impact on municipal waste management programs. In this work, three lowtech composter prototypes were designed and built using discarded metallic oil drums and recycled plastic materials. The composting experience was carried out at an oilfield, using food waste from a catering service for 65 people. Temperature was used as the main indicator of the composting process, and final product quality was characterized through the following variables: total nitrogen, total phosphorous, extractable phosphorous, pH, organic matter and electrical conductivity. Results confirm the effectiveness of this composting technology for organic waste treatment: thermophilic temperatures were reached in all prototypes, and final products obtained from all composters showed high nutrient and organic matter contents, but also high pH and electrical conductivity values, which frequently appear in decentralized composting product; however, obtained values are still adequate for agronomic applications. Nevertheless, some significant differences were found for these variables among the prototypes, possibly related to design characteristics. Finally, composters construction could be optimised by recycling other waste, as shown in this experience (metallic drums, high density polyethylene and accessories), in order to improve the strategies for decentralised composting.