Case Story China

Biogas production from kitchen wastes in Jinhua, China

December 2021

Production of valuable products from kitchen wastes

In China, especially in urban areas, a significant quantity of kitchen waste is generated annually. Jinhua is a city of c. 7 million people located in Zhejiang Province, China. The city has an ambition to improve the quality of the urban environment and achieve the UN sustainable development goals such as SDG 6 (Clean Health and Water), SDG 7 (Affordable and Clean Energy), and SDG 11 (Sustainable Cities and Communities). A commercial project entitled Jinhua Kitchen Waste Biogas Plant was launched on June 27, 2016, with the primary goal of treating kitchen wastes and producing biogas in the process.

The project uses single-stage anaerobic digestion technology, including two parallel continuous stirred tank reactors (CSTR), each with a working volume of 1200 m3 (Figure 1). The raw materials are kitchen wastes from c. 1700 restaurants and canteens in Jinhua City. The biogas project processes 100 t of kitchen wastes per day at a total solids (TS) concentration in the range 6.79% to 8.92%. Volatile solids (VS) account for 79.79% to 83.63% of the total solids. The average daily biogas production has been recorded as 3944 ± 566 m3/d. After the biogas is desulfurized, around a quarter of the produced biogas is used onsite to provide energy for the industrial process and in doing so substitute for fossil fuel. The remaining biogas is sold directly for electricity generation at a rate of 0.35 RMB/m3 .

To optimize the process and to gain a competitive market advantage, the project uses filtered non-water-soluble (non-biodegradable) kitchen waste fines (typically 15 to 20% of the yield of kitchen wastes) for breeding Black Horsefly (which is a nutritious animal feed); this creates a revenue of the order of 3 million RMB/y. The crude oil extracted from kitchen wastes (about 1825 t/y) is sold directly, generating further revenues of 9 million RMB/y