Comparative Study on Biowaste Definition: Effects on Biowaste Collection,Composting Process and Compost Quality

A comparative study was run during 13 months on two biowaste definitions involving both lab tests and field surveys. A narrow biowaste definition, allowing only biogenic wastes (kitchen and garden waste) and referred to as ‘Biowaste,’ was compared to a broad biowaste definition, referred to as ‘Biowaste Plus’ and including man-made products, such as nonrecyclable wastepaper and diapers. Two similar test areas, each with about 425 inhabitants, were defined in a semiurban area north of Antwerp. During the entire test period, the amount of curbside waste (i.e., biowaste and restwaste or ‘grey waste’), was continuously measured and analyzed regularly (twice per season) for composition. At the start, middle and end of the test, the population of each test area was surveyed. Bench-scale aerobic composting experiments were run to evaluate the influence of both biowaste definitions on the composting process and the compost end product.

The introduction of source separated waste collection resulted in an overall landfill diversion rate of 43 percent for the (narrow) ‘Biowaste’ definition and 46 percent for the (broad) ‘Biowaste Plus’ definition. The contamination of biowaste with restwaste was low for both definitions (about three percent). Assuming that the collection and the appropriate disposal of organics could be improved to 95 percent efficiency (compared to about 60 percent currently), the landfill diversion rate could be increased to 59 percent for the ‘Biowaste’ and 74 percent for the ‘Biowaste Plus’ definition. Whereas the average sorting efficiency of separately collected organics was about 61 percent; 49 percent for nonrecyclable paper; and as low as 20 percent for certain categories of nonrecyclable paper (e.g., nonrecyclable cardboard packages). Apparently more education or a better systém of recognition and identification is needed to improve the collection efficiency of man-made compostables. Indeed, for easily recognizable products such as diapers, the sorting efficiency was as high as 70 percent.

The acceptance and goodwill of the population was significantly higher for the ‘Biowaste Plus’ definition, especially in the summer months. The yearly, overall composition of the total curbside waste (biowaste and restwaste combined) was 17 percent kitchen organics, 47 percent yard waste, four percent recyclable paper, 13 percent nonrecyclable paper and 19 percent noncompostables. It must be mentioned that glass, paper and large yard waste were collected separately by a voluntary bring-system. Biowaste Plus typically contained 16.0 percent paper (of which 2.9 percent was recyclable) versus 2.0 percent for Biowaste (0.3 percent recyclable).

The ‘Biowaste Plus’ definition resulted in improvements for the aerobic composting process due to easier moisture control, better aeration and a more tempered pH evolution. A significant difference was seen for NH₃ and corresponding odor emission, both being much lower with ‘Biowaste Plus.’ The quality of the compost produced was similar and acceptable for both biowaste definitions, according to existing standards (VLACO in Flanders and RAL in Germany).