Effects of bulking agents, load size or starter cultures in kitchen-waste composting

Background: To prevent the interruption of the carbon cycle by the disposal of waste to landfills, organic kitchenwaste requires proper treatment such as composting to reduce its uncontrolled degradation on disposal sites andsubsequent greenhouse gases, odour emissions and nutrient losses. This study investigated the effects of bulkingagent, newspaper and onion peels, composting waste load sizes of 2 and 6 kg, or the use of starter culture onkitchen-waste composting consisting of nitrogen-riched substrates, vegetable scraps and fish processing waste inan in-vessel system. The optimised formulation of kitchen waste mixture was used for a 30-day composting study,where the temperature profiles were recorded and the carbon-to-nitrogen ratios were measured as an indication ofcompost maturity. The kitchen-waste composting process was conducted in parallel in two fabricated kitchenwaste composters.Results: It was found that the onion peels were more suitable in producing matured compost where the carbon-to-nitrogen ratio reduced to 10 within 16 days of composting. A smaller kitchen waste load size of 2 kg gave ashorter composting time by half when compared to the 6 kg. The use of a microbial cocktail consisting seven typesof bacteria and eight types of fungi isolated from soils as a starter culture for this kitchen-waste composting did notshow advantages in accelerating the composting process.Conclusions: The results suggest that the in-vessel kitchen-waste composting can be efficient with a minimal loadof about 2 kg using onion peels without additional starter culture.