Sewage sludge-highland barley straw composting in the Tibetan plateau: an experimental and simulative study

The huge output of sewage sludge (SS) has become a severe issue for the vulnerable environment of the Tibetan plateau. Composting is a considerable way to answer the SS yield increment and recycle the nutrients. However, the application of composting is limited by the oxygen-deficient environment in Tibet. In this study, the feasibility of applying composting to Tibet was investigated by experiment and simulation. The SS and highland barley straw (HBS) composting was conducted under different aeration rates (ARs). Fourier-transform infrared (FTIR) spectroscopy and germination index (GI) analysis were applied to assess the maturity and stability. Moreover, a water-waste-nutrient nexus model was established on the basis of experimental data and the actual environmental conditions to estimate the environmental impacts and the economic value of composting in Tibet. The experimental results showed that best performance was obtained when AR was 0.42 L min(-1) kg(-1) in the initial stage and 0.69 L min(-1) kg(-1) in the thermophilic stage. The modelling results showed that applying the compost as a soil amendment could effectively reduce the application of chemical fertilizer, as well as N (12.66%) and P (7.14%) loss from the farmland soil. The annual economic benefit of applying SS/HBS compost fertilizer was 4.53E + 5 CNY (7.02E + 4 $), which correspondingly increased as the SS yield increased. The results provided reliable references for the application of composting in Tibet, and the nexus model offered an effective way to assess the economic potential of composting, which supported the decision making of waste treatment and nutrient recovery in Tibet.