A low impact sediment and green waste co-compost: can it replace peat in the nursery sector?

Co-composting is suitable technology for recycling dredged sediments (S) and green wastes (GW), whose recovery are limited by their contamination and variability in composition, respectively. Some limitations in the process have been previously detected (e.g., limited thermophilic phase and low organic carbon content in the final product), thus restricting the use of co-compost for agricultural purposes. To optimize the co-composting and extend the application of the co-compost, the GW content in the piles (3S:1GW, 1S:1GW and 1S:3GW) and the pile volumes was increased. At the end of the process, the co-compost properties were compared to current legislation. The co-composting’s impact on the environment and its possible replacement of peat were also assessed by LCA. Maturity and stability were reached in all piles: enzyme activities (< 2214–39 μmol g− 1 h− 1), electrical conductivity, total organic carbon, phytotoxicity (GI > 100%) decreased, together with hydrocarbons (− 162%/− 48%) and PCB (< 0.01 mg/kg). The gas emissions derived from waste recovery ranged from 22 to 25 kg m− 3 CO2eq. The increased GW in the piles extended the thermophilic phase, improving the co-compost sterilization and agricultural application. 1S:3GW was in line with international and national fertilizer regulations. 3S:1GW and 1S:1GW were compliant with international limits, but not with national regulations regarding conductivity, bulk density and total organic carbon content. Mixing them with an organic matter source would reach the legislative thresholds. Increasing the GW amount in the co-compost piles, therefore, improved the S-GW co-composting and suggests using this co-compost as a sustainable and legally applicable fertilizer.