The Migration and Transformation of Heavy Metals in Sewage Sludge during Hydrothermal Carbonization Combined with Combustion

Table 3

Concentrations of leachable HMs in the TCLP tests (mg/kg).

HMs	Raw SS	SS-220-1h	SS-220-2h	SS-220-3h	SS-250-1h	SS-280-1h	Permissible limits^a
Cr	0.11±0.00	0.61±0.01	0.44±0.01	0.39±0.01	0.09±0.00	0.09±0.00	5.0
Mn	231.06±10.67	289.22±10.56	293.71±12.45	446.73±16.56	536.53±16.78	449.39±14.34	---^b
Ni	5.41±0.23	6.73±0.25	1.53±0.07	1.10±0.05	0.68±0.01	0.72±0.01	5.0
Cu	1.42±0.06	0.41±0.01	0.18±0.01	0.09±0.00	0.12±0.01	0.04±0.00	---^b
Zn	30.32±1.67	38.62±2.12	32.18±1.68	30.97±1.56	13.77±0.53	14.62±0.68	5.0
As	25.57±0.48	20.42±0.59	12.01±0.43	7.97±0.25	10.34±0.38	6.16±0.21	5.0
Cd	0.05±0.00	0.03±0.00	0.04±0.00	0.03±0.00	0.03±0.00	0.01±0.00	1.0
Pb	0.03±0.00	0.02±0.00	0.03±0.00	0.02±0.00	0.08±0.00	0.01±0.00	5.0

(1) a: USEPA, test methods for evaluating solid waste: physical/chemical methods (SW-846).
(2) b: Not titled.