Rotary drum composting of different organic waste mixtures
The effects of three different mixtures of organic waste on composting in a rotary drum were examined by measuring changes in physico-chemical and biological parameters. It was observed that the time courses of the three mixtures: run A (grass cuttings, vegetable waste and food waste), run B (cattle manure, vegetable waste and sawdust) and run C (cattle manure, food waste, vegetable waste, paper waste and sawdust) were quite diverse. Run B, with initial C/N ratio 22 and containing a large proportion of cattle manure produced high quality and mature compost within 20 days. It showed a final total nitrogen (2.1%), final total phosphorus 3.52 g kg—1, final total organic carbon (TOC) (24.8%) and final moisture content (44%). At the end of 20 days, higher degradation led to final chemical oxygen demand (COD) (454 mg L— 1), biochemical oxygen demand (BOD) (107 mg L— 1), fecal coliform (1.2 x 102 bacteria g— 1), fecal streptococci (85 bacteria g—1) and low electrical conductivity (1.658 dS m—1), respectively. Furthermore, run C with initial C/N ratio of 30 and containing a larger amount of food and vegetable waste produced good quality compost and resulted in 4.34% total nitrogen and 2.42% total phosphorus after 20 days, but, it had higher final fecal coliform 2.5 x 104 bacteria g —1, fecal streptococci 2.1 x 104 bacteria g—1, high TOC and NH4-N and a BOD/COD ratio of 0.63, which rendered it hygienically unsafe and immature. Finally, run A with initial C/N ratio of 15 showed a higher amount of EC (4.84 dS m—1), NH4-N, BOD/COD ratio of 0.4 with 15% nitrogen loss, which indicated an unstable product even after 20 days of composting. Therefore, it was found that rotary drum composting of a combination of cattle manure, vegetable waste and sawdust resulted in a primary stabilized compost within 20 days of composting.