Silage and flue gas desulfurized gypsum as additives improve green waste composting

Abstract

Although composting is an environmentally safe and efficient way to dispose of and stabilize green waste (GW), the composting of GW generally takes a long time due its high lignocellulose content. To reduce the composting period and increase compost quality, an L9 (34) orthogonal experiment was conducted to assess the effects of silage (SG; 0, 25, 45 %) and flue gas desulfurization gypsum (FGDG; 0 %, 2.5 %, and 5 %) as additives on GW composting. Treatments differed in the quantities of SG and FGDC added, but all treatments received the same quantities of urea (24 g per kg of GW dry weight) and microbial inoculum (5 ml per kg of GW dry weight) at the start of the composting process. The results indicated that the addition of SG or/and FGDG accelerated the composting process and increased the maturity and nutrient contents of the compost product. According to a multi-index matrix analysis, the optimal combination of SG and FGDG was 45 % SG and 2.5 % FGDG. The optimal treatment resulted in a compost product with a coarseness index of 35.47, a germination index of 263 %, and the following contents (mg/kg) of total Kjeldahl nitrogen, total phosphorus, total potassium, NO3--N, available phosphorus, and available potassium: 35,634, 10,937, 13,243, 13.27, 143.51, and 8873.36, respectively. The optimal combination of SG and FGDG reduced the composting of GW to 28 days and produced a stable and high-quality compost product.