The use of MSW-compost on land, a study of metal and nutrient leaching

It is estimated that up to 138 million tonnes of bio-waste are produced in Europe annually, with only 25% being recycled into high-quality compost and digestate. Currently, residual organic waste is generated as by-product of municipal solid waste treatment. Its reuse options vary across EU countries, due to the lack of clear guidance at European level. In some countries, compost derived from municipal solid waste (MSW – compost) is restricted to being used as landfill cover or in land reclamation, under the premises of meeting national legal criteria. Other countries, have regulated its used as marketable compost if it meets defined compost standards. However, for many countries the value-added use of MSW derived compost is uncertain.

The restricted use of MSW - compost is linked to the organic and inorganic contamination associated with such a heterogeneous material. Despite this, under the European view of the Circular Economy, MSW-compost has great potential to be reused and recycled for the benefit of all. Controlled use on land would off-set carbon emissions by diverting the material from a waste that is largely incinerated or added to landfill to a carbon positive soil additive that increases soil quality particularly in restoration sites. 

Our study aims to risk-assess the use of MSW-compost as a soil amendment by monitoring resulting water run-off for metal and nutrient content. Leaching trials, conducted over 6 months were performed in a forest soil (20 cm depth) with a history of Sitka Spruce plantation (c.a 20 years). Adapted water storage tanks were set-up to conduct the trials. Leachate was collected weekly in the first two months, and monthly thereafter. Four treatments 1) control, 2) sewage sludge chemically stabilized (10 t/ha), 3) MSW-compost (10 t/ha) and 4) MSW-compost (25 t/ha) were established in duplicate. Sewage sludge was used as a comparison material, due to its current legal status allowing for controlled land spreading. Leachate samples were analysed for nitrate, ammonium and the metals aluminium, cadmium, copper, total chromium, mercury, nickel, zinc and lead. 

Preliminary results from the first 6 weeks show that metals concentrations in the leachate from all trials were below threshold criteria in surface water quality regulations. Levels of ammonium above detection limits were only detected at week one and surpassed 0.2 mg/L. Nitrate concentration in the leachates was found to be below 50 mg/L and it peaked in the sewage sludge and MSW-compost (25 t/ha) at week 2.

Results gathered so far show that the use MSW-compost in land compares to sewage sludge application in relation to their potential for water pollution. MSW-compost could be used as a soil improver under a regulatory alignment similar to the sewage sludge regulations, aligned with the current European Circular Economy goals.