Inside the small-scale composting of kitchen and garden wastes: Thermal performance and stratification effect in vertical compost bins

Abstract

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.

Decentralized Community Composting: Past, Present and Future Aspects of Italy

“…The main advantages of decentralized composting over centralized systems are summarized in Table 1. In a broad perspective, decentralized composting can help to decrease the cost and effort for transportation of waste for processing and treatment, and further reduce the need to construct new disposal facilities, enable local reuse of organic matter, create local small-scale enterprises as well as reduce costs associated with commercial fertilizer purchase [19,53,54]. Furthermore, the final compost product is comparatively of higher quality due to efficient separation and less intercontamination of wastes [55,56].…”

“…Community composting reactors can be different, in other words, "simpler", than centralized composters. Plastic bins in any shapes (i.e., rectangular, cylindrical, conical) are often used for community composting reactors [7,54]. Plastic drum reactors were also recently reported [59].…”

Proportions of Organic Waste in the Process of Composting

“…The temperature variation in the composting process Figure 2 didn't occur as described in the literature, where it shows that in the first stage, the temperature is around 40ºC, then in the second phase, thermophilic, it acts between 65º-70ºC and final stage of maturation, the temperature gradually decreases. This may have been influenced by the proportions of the residues, since even in winter (May to October), when the temperature ranged from 8 to 33 °C Figure 3, Arrigoni, et al [18] in Argentina, where the average annual temperature is 8.4 °C, performed a work with composting and the temperature of the process varied according to the literature. Several authors have observed different behavior of temperature in the composting process, this indicates that average values of temperature should not be considered as standard [19]; [20]; [21]; [22]; [23]; [24].…”

Co-composting of Petroleum Sludge with Poultry Manure

“…The process of composting can be used for different types of wastes such as on animal manures [25], food wastes [27], kitchen and garden wastes [28], sewage sludge [29], household organic waste [30] etc. However, studies shown some different methods of composting previously.…”