Nitrogen fixation additive reducing emission of NH3 and H2S during composting of kitchen waste and cornstalk

Abstract: In order to reduce odor emissions such as NH3 and H2S, this study designed experiments to investigate the effects of H3PO4+Mg(OH)2, Ca(H2PO4)2, FeCl3, and β cyclodextrin on producing and releasing NH3 and H2S during kitchen waste composting. The composting treatment without adding chemical materials was used as control. The kitchen waste consisted of 53% vegetation waste, 24% fruit wall, 19% meat, and 4% leaves. For all treatments, cornstalks as an additive using the wet weight ration of 1:5.7 were added to the kitchen waste composting. All treatments were analyzed using 60 L heat insulated composting vessels with forced aeration systems. The vessels were controlled by the C-LGX program, which enables aeration to be controlled automatically by time or inside temperature. Aeration consisted of pumping ambient air into the reactor continuously at a rate of 0.2 L/(kg·min) dry matter.The TKN and TOC were determined according to the Chinese national standard (NY 525-2002). The pH, EC, and GI were determined in water extracts (20 g of dry weight compost were extracted with 200 ml of distilled water, stirred for 1 h, and then centrifuged at 4000 rpm). pH value was measured with a pH meter, electrical conductivity (EC) was measured by a DDS-12A conductivity meter. The moisture content was determined by drying the samples at 105℃, until the weight was unvarying. The boric acid titration method was used to determine ammonia emission. The H2S content was analyzed daily using a portable biogas analyzer. Composting gas samples were extracted using a suction pump (built-in biogas analyzer, gas flow: 550 mL/min), and then transferred to the inlet port of the biogas analyzer via a Teflon hose that contained a filter element (2.0 μm PTFE) installed in the middle of the pipe. The measurement was taken for about 90 seconds, and the measured value of H2S was read directly from the screen.The results showed that adding nitrogen control material reduced the pH of the composting systems, and the loss rate of the composting materials obviously decreased compared with CK. The analysis of phytotoxicity indexes of EC and GI showed that all treatments reached the compost maturity requirements. Four kinds of control materials could all decrease NH3 and H2S emissions, but the reduction mechanism are not the same. Compared with treatment CK, the cumulative emissions of NH3 were reduced by 49.5%, 38.5%, 64.2%, and 62.7%, and the cumulative emissions of H2S were reduced by 39.2%, 5.9%, 52.0% and 47.8% for the treatments of P+M, CaP, FC, and CD, respectively. After integrating the reduction of NH3 and H2S emission and the phytotoxicity of compost, FeCl3 was the best nitrogen and sulfur conservation material during kitchen waste composting in this work. This study can provide a reference for the screening of odor control materials in a kitchen waste composting process.