Quality of separately collected bioorganic municipal waste and BMW compost of Shenyang, China
Precautionary thinking requires with regard to the application to soils of BMW compost that the compost is as ‘clean’ as possible.
As an intrinsic part of a sustainable economy bioorganic wastes, as far as it is possible and appropriate, should be materially utilised. Municipally generated and collected solid bioorganic waste, or bioorganic municipal waste, should be biotechnologically stabilised, i.e. composted, preferably subsequently to fermentation, and the compost should be used as a fertiliser or soil conditioner, at the same time further reducing the extent of application of mineral fertilisers. The bioorganic fraction of Municipal Solid Waste (MSW) causes extensive greenhouse gas emissions of methane and carbon dioxide if disposed of onto landfills whilst this methane could be used as a renewable energy source in form of biogas generated by controlled fermentation.
The major objectives of the Sino-German research project ‘Resource Recovery and Utilisation of Bioorganic Municipal Waste’ (RRU-BMW), which was carried out in the Chinese city Shenyang, capitol of the province Liaoning in northeastern China, were to ascertain the quantity, composition, biodegradability, methane formation potential and pollution level of the bioorganic fraction of Municipal Solid Waste collected from households as well as the attitude of the inhabitants towards advanced waste management.
Eight identical laboratory composting reactors were equipped with thermal insulation, controlled forced air supply, monitoring systems for temperature and exhaust air composition, and exhaust air collection with subsequent air treatment in a biofilter. Preliminary experiments have led to optimised experimental conditions of addition of 10 % (m/m) of structure material (ground maize straw, ‘straw’) and 21 d run-time. All eight reactors have been run in parallel under identical external conditions, and the temperature in the reactors and the concentrations of oxygen and carbon dioxide in the exhaust air have been monitored through semi-continuous measurements. BMW from 4 pilot areas, 3 applying primary and 1 applying secondary source separation, was composted. 25 samples have been taken during the course of the experiments of each of the composting reactors. The wet and dry samples were analysed for standard parameters and the concentrations of copper, AOX and PAHs. Samplings, including homogenisation, and measurements were carried out according to national and international standards. For the analysis of copper concentrations, the samples were extracted by means of microwave-assisted acid digestion. The concentrations of heavy metals in the extracts have then been measured by means of flame atomic absorption spectrometry (FAAS).
None of the concentrations or sum of concentrations of benzo(a)pyrene (BaP), 16 PAHs according to U.S. EPA (≤ 3.26 mg/kg dm), 6 PAHs according to the German drinking water ordinance (< 0.08 mg/kg dm), 15 PAHs according to the German soil protection ordinance (≤ 2.95 mg/kg dm) or AOX (≤ 230 mg/kg dm) exceeded the existing or proposed Chinese, EU, German or Austrian limit values for pollutants in sludge for agricultural use in any case. The data also show a low to very low contamination with copper (Cu, ≤ 29.4 ± 4.9 mg/kg dm). No systematic significant differences between the concentrations of contaminants in bioorganic municipal waste (BMW) or BMW compost from either primary or secondary source separation have been observed. In addition, the average proportion of nonbioorganic (ballast & foreign) matter amounted to 3.6% (m/m wm) (Raninger et al., 2006). These levels of pollution are comparably high or even lower than in Europe and Germany. Thus, the results presented here demonstrate that the compost derived from BMW collected by source separation of household MSW in Shenyang, China, would be well applicable as fertiliser or soil conditioner.
