Decontamination of anaerobically digested slurry in a paddy field ecosystem in Jiaxing region of China

Anaerobic digestion has become increasing popular for managing biowastes in rural China as it has the advantage of generating biogas, a renewable energy. A new challenge, however, is minimizing the environmental pollution resulting from the anaerobically digested slurry (ADS). The aim of this study was to assess the feasibility of using a paddy field to remediate ADS while simultaneously cultivating rice. A field experiment was trialed using six treatments based on varying nitrogen loadings over the period of a rice-growing season. These treatments were adjusted to the content of the N within the ADS and had loadings of 270, 405, 540 and 1080 kg N ha−1. These treatments were compared to a negative control (no fertilizer) and a positive control (chemical fertilizer) that consisted of urea applied at 270 kg N ha−1. The effects of these N sources and slurry remediation were monitored using standard methods to measure water quality, soil properties and changes in rice production. Rice grain yields were generally higher for all ADS treatments than for the urea N treatment. Standing water quality in the field could reach national discharge standards for all treatments within 7–8 days after each ADS irrigation. Groundwater quality and heavy metal concentrations in both soil and the rice grain were not affected by the ADS treatments. We suggest that the quantities of ADS irrigated in 867–1734 m3 ha−1 was not only safe for food quality (rice grain) and the receiving environment (water and soil), but also beneficial to soil fertility and rice grain yield.

► This study assessed the digestion potential of ADS in a paddy field ecosystem.
► Rice grain yields were generally higher for ADS treatments than for urea treatment.
► Water quality in the field can reach National Standards within 8 days after ADS irrigation.
► Heavy metal content in soil and rice grain was not affected by the ADS treatments.
► The maximum safe amount of ADS irrigation was in 1734 m3 ha−1 for a rice growth season.