Microbiological Evaluation of the Effectiveness of Sewage Sludge Sanitization with Solar Drying Technology

Table 3

Average results of physicochemical analyses of sewage sludge in winter cycles.

		Average results for winter cycles (replications number = 3)
Parameter	Unit	Sampling terms for the research (days)
		0	7	14	21	28
Sludge dry matter after centrifuge	%	13.86 (±0.62)*	—	—	—	—
Sludge dry matter in the pile	%	—	18.90 (±3.21)	21.43 (±4.33)	25.12 (±3.93)	24.54 (±4.84)
Organic substance	% D.M.	64.20 (±2.17)	65.50 (±2.04)	64.20 (±2.65)	63.40 (±2.87)	62.40 (±3.50)
pH	—	6.90 (±0.06)	6.90 (±0.06)	7.00 (±0.11)	6.98 (±0.10)	6.90 (±0.06)
Total nitrogen content	% D.M.	2.10 (±0.15)	2.12 (±0.17)	2.00 (±0.06)	2.12 (±0.17)	2.09 (±0.23)
Ammonium nitrogen content	% D.M.	0.10 (±0.06)	0.10 (±0.06)	0.11 (±0.04)	0.09 (±0.03)	0.15 (±0.01)
Total phosphorus	% D.M.	2.20 (±0.12)	2.22 (±0.13)	2.21 (±0.11)	2.20 (±0.12)	2.20 (±0.12)
Calcium content (Ca)	% D.M.	1.15 (±0.03)	1.13 (±0.03)	1.12 (±0.02)	1.15 (±0.03)	1.15 (±0.03)
Magnesium content (Mg)	% D.M.	0.23 (±0.04)	0.23 (±0.04)	0.23 (±0.04)	0.34 (±0.05)	0.23 (±0.03)
Heavy metals
Lead (Pb)	mg/kg D.M.	22.23 (±2.79)	22.20 (±2.76)	22.20 (±2.76)	22.20 (±2.76)	22.20 (±2.76)
Cadmium (Cd)	mg/kg D.M.	1.98 (±0.26)	1.97 (±0.21)	1.89 (±0.20)	1.89 (±0.20)	1.87 (±0.18)
Mercury (Hg)	mg/kg D.M.	0.05 (±0.03)	0.05 (±0.03)	0.05 (±0.03)	0.00 (–-)	0.05 (±0.03)
Nickel (Ni)	mg/kg D.M.	19.50 (±1.94)	19.50 (±2.12)	19.50 (±1.94)	19.50 (±1.94)	19.50 (±1.94)
Zinc (Zn)	mg/kg D.M.	1248.00 (±131.15)	1248.00 (±131.15)	1248.00 (±131.15)	1249.00 (±125.87)	1250.00 (±126.26)
Copper (Cu)	mg/kg D.M.	220.70 (±17.43)	220.70 (±17.43)	220.70 (±17.43)	220.70 (±17.50)	220.70 (±17.43)
Chromium (Cr)	mg/kg D.M.	27.64 (±2.08)	27.64 (±2.08)	27.64 (±2.08)	27.64 (±2.08)	27.64 (±2.08)

*Standard deviation.