Impact of compost and manure on the ripening of dredged sediments

Purpose: In low lying areas with dense networks of canals for land drainage, sediments accumulate in the waterways and have to be periodically dredged. These adjacent areas are mainly used for farming and agriculture and suffer from high rates of subsidence. The recycling of organic amendments, such as sediments, compost and manure, in agricultural soils can improve plant growth and yield, soil carbon content, and microbial biomass and activity, and have the potential to reverse the process of land subsidence. Materials and methods: The effect of mixing bio-waste compost and the solid fraction of swine manure with dredged sediments before dewatering and biochemical ripening was investigated in terms of type and quantity of organic matter, CO2 production and O2 consumption, and N, P and S content. The water released during dewatering, the aggregate stability, and the undrained shear strength after ripening were also assessed since these areas have to be assessable by trucks and cattle. Results and discussion: For the sediment with compost and manure the transformations in the type of organic matter, CO2 production and O2 consumption were larger compared to the individual fractions, indicating a positive priming effect. Most volume lost during ripening can be attributed to the loss of water and not to the loss of organic matter. In addition, the mixtures result in very stable aggregates and showed an undrained shear strength three times higher than measured for the sediments. Conclusions: Sediments, compost and manure can be used and applied as beneficial use to reverse the process of land subsidence in low lying areas.