Potential use of solar energy for waste activated sludge treatment

Figures & data

Figure 1 Solar pilot plant.

Figure 2 Evolution of COD for WAS as a function of solar oxidation time in different months. Inner: monthly average solar radiations during 2009.

Figure 3 Percentage COD and TSS removals during sludge solar oxidation under clear and cloudy sky condition.

Table 1 Operational conditions of sequential solar oxidation & biological treatment processes.

#	Process	Time of solar oxidation (min)	Time of biological treatment (hr)	[TSS]i (g/L)	[COD]i (mg/L)
SQ1-SOL-JUN				4.74 ± 0.06	480 ± 5
SQ1-SOL-MAR SQ1-SOL-SEP	Solar oxidation+biological treatment+ Solar oxidation+biological oxidation	120	24	4.74 ± 0.06 4.74 ± 0.06	480 ± 5 480 ± 5
SQ2-SOL-JUN SQ2-SOL-MAR SQ2-SOL-SEP	Solar oxidation+biological treatment+ Solar oxidation+biological oxidation	120	Bio1 = 48 Bio2 = 96	4.24 ± 0.06 4.75 ± 0.06 4.61 ± 0.06	444 ± 5 428 ± 5 440 ± 5
SQ3-SOL-JUN SQ3-SOL-MAR SQ3-SOL-SEP	Solar oxidation+biological treatment+ Solar oxidation+biological oxidation+solar oxidation	240	Bio1 = 24 Bio2 = 96	4.54 ± 0.06 4.64 ± 0.06 4.74 ± 0.06	445 ± 5 456 ± 5 476 ± 5
SQ4-SOL-JUN^a SQ4-SOLMAR^a SQ4-SOL-SEP^a	Solar oxidation+biological treatment+ Solar oxidation+biological oxidation	120	Bio1 = 24 Bio2 = 48	4.70 ± 0.06 4.70 ± 0.06 4.70 ± 0.06	490 ± 5 490 ± 5 490 ± 5
^a Mixed sludge (25% fresh sludge).

Figure 4 Evolutions of COD and % COD removal during sequential solar oxidation & biological treatment (a) SQ1, (b) SQ2 and (c) SQ3.

Table 2 Experimental results obtained during sequential WAS oxidation.

#	Percent of COD	Percent of TSS	Percent of sludge settled in 30 min	SFI (s/g)
SQ1-SOL-JUN	9.8	9.3	40	45
SQ1-SOL-MAR	8.8	8	58	63
SQ1-SOL-SEP	7.1	7.9	65	77
SQ2-SOL-JUN	10.1	9.8	48	33
SQ2-SOL-MAR	9	8.8	60	54
SQ2-SOL-SEP	7.2	8	67	68
SQ3-SOL-JUN	16	13	38	28
SQ3-SOL-MAR	11.5	12	52	47
SQ3-SOL-SEP	8.3	10	60	49
SQ4-SOL-JUN	23	27	60	55
SQ4-SOL-MAR	16	20	78	68
SQ4-SOL-SEP	15	18	85	70

Figure 5 Effect of single solar oxidation on SFI of sludge. Insert sludge volume index during solar oxidation.