Composting of municipal solid waste by different methods improved the growth of vegetables and reduced the health risks of cadmium and lead

Reutilization of putrescible municipal solid wastes (MSW) in agriculture can provide valuable plant nutrients. However, it may pose serious noncarcinogenic health risks for a human when contaminants, especially the heavy metals in MSW, end up in plants through the waste-soil-plant continuum. This study examined the effects of composting methods viz. aerobically (AC), anaerobically (ANC), and aerobic-anaerobically (AANC) composted MSW material on (i) fertilizer value: vegetable yield, nitrogen (N) mineralization, and apparent N recovery (ANR); and (ii) associated health risks: selected heavy metal concentration, daily intake of metals (DIM), health risk index (HRI), hazard index (HI), and target hazard quotient (THQ) when applied to a loamy soil. All the aforementioned compost materials were incorporated into the sandy loam soil filled in pots and carrot and spinach were cultivated for 85 and 90 days, respectively. After soil application, between 51 and 56% of the applied organic N was mineralized from ANC material, while the values in case of AC and AANC were 26–31% and 34–40%, respectively. Consequently, dry matter yield and vegetable N uptake from composts were in the order ANC > AANC > AC (P < 0.05). Further, vegetable ANR was the highest from ANC (56 and 56%) than AANC (42 and 45%), and AC (30 and 33%) for spinach and carrot, respectively (P < 0.05). Interestingly, plant uptake of lead and cadmium was lowest from ANC as compared to AC or AANC (P < 0.05), irrespective of the vegetable type. Consequently, DIM, HRI, and THQ for these metals were substantially lower in the former as compared to the latter compost materials. Further, HI from ANC material was 50% lower over the unfertilized control indicating the absence of noncarcinogenic human health risks via vegetable intake. This all indicates that from viewpoint of sustainable waste recycling in agriculture, anaerobic composting is superior to the other composting methods.