From anaerobic to aerobic treatment: upcycling of digestate as a moisturizing agent for in-vessel composting process

Bioresources and Bioprocessing

Table 1 Physico-chemical characterization of the collected digestates

Parameters	Units	D1	D2	D3	D4	D₁ (Stoknes et al. 2016)
pH	–	7.49	7.51	7.02	8.13	–
Moisture content (MC)	% of FM	96.70	95.90	97.50	97.30	97.60
Carbon (C)	% of FM	37.60	35.20	40.10	37.20	–
Nitrogen (N)	% of FM	2.90	3.70	4.70	4.40	10
C:N ratio	–	12.97	9.51	8.53	8.45	–
Phosphors (P)	% of TS	3.02	3.17	2.87	2.91	1.00
Potassium (K)	% of TS	4.16	4.04	4.21	4.86	4.00
Lead (Pb)	mg/kg TS	2.33	2.46	2.29	2.54	0.43
Copper (Cu)	mg/kg TS	38.86	46.02	44.07	60.02	–
Zinc (Zn)	mg/kg TS	165.64	185.07	167.65	223.41	75.00
Nickel (Ni)	mg/kg TS	8.08	7.24	6.48	9.00	225
Cadmium (Cd)	mg/kg TS	0.32	0.40	0.35	0.38	8.94
Arsenic (As)	mg/kg TS	1.40	1.95	1.70	1.76	0.14
Mercury (Hg)	mg/kg TS	0.02	0.05	0.07	0.09	–

FM fresh matter, TS total solids, D₁ digestate collected from mesophilic anaerobic digesters treating FW (Stoknes et al. 2016)