Co-digestion of sewage sludge and wood fly ash

Figures & data

Table 1. TS, VS and COD of the thickened and digested sludge from Luleå sewage treatment plant from a sample taken after performing the experiments.

	TS [%]	VS [%TS]	COD [g/l]
Thickened sludge	3.5	76.8	39.3
Digested/thin sludge	2.8	63.4	23.4

Table 2. Elemental analysis of the used fly ash.

Major constituents	Content [%TS]	Trace elements	Content [mg/kgTS]
SiO2	25.7	As	6.22
CaO	32.3	Cd	9.63
K2O	7.38	Cr	56.2
MgO	4.22	Cu	114
Na2O	1.43	Hg	<0.01
P2O5	3.04	Ni	34.5
		Pb	153
		S	25,700
		Zn	3280

Table 3. Gas analyses showing the methane to carbon dioxide ratio and hydrogen sulphide content of produced biogas in experiments with and without ash addition.

Experiment	CH4/CO2 ratio	H2S
Sludge without ash addition	2.0	0.0%
Sludge with 0.4 gash/gVS ash addition^a	2.8	0.6%
Sludge with 0.7 gash/gVS ash addition	3.8	0.9%

^a Also includes results of initial screening tests with additional leachate addition.

Figure 1. Accumulated methane production of the thickened sludge of two screening-test experiments as examples.

Table 4. pH levels and EC measurements at the beginning and end of experiments with and without ash addition.

Experiment	pH begin	pH end	EC begin [mS/cm]	EC end [mS/cm]
Sludge without ash addition	7.43	7.45	6.58	11.62
Sludge with 0.4 gash/gVS ash addition	8.27	7.53	7.30	13.46
Sludge with 0.7 gash/gVS ash addition	8.78	7.71	7.60	14.41

Figure 2. Normalized coefficients of MODDE, showing how different types of sludges affected plant growth.