Comparison of physicochemical parameters during the forced-aeration composting of sewage sludge and maize straw at different initial C/N ratios

Figures & data

Table 1. Selected physicochemical properties of digested sludge and maize straw

Parameter	Sewage Sludge^a	Maize Straw^a
pH	8.09	7.15
Moisture content (%)^b	70.00	10.00
Total organic carbon (g kg^−1)^c	235.41	560.92
Total nitrogen^a (g kg^−1)^c	21.03	8.01
C/N ratio	11.21	70.11
Notes: ^aValues are means of triplicates. ^bWet-weight basis. ^cDry-weight basis.

Figure 1. Change of temperature during composting of sewage sludge and maize straw at different initial C/N ratios. (a) C/N ratio of 25; (b) C/N ratio of 20; (c) C/N ratio of 14.

Figure 2. Change in pH and EC during the composting of sewage sludge and maize straw at different initial C/N ratios. Error bars represent standard deviation. (a) pH; (b) EC.

Figure 3. Change in NH₄ ⁺-N and NO₃ ⁻-N during composting of sewage sludge and maize straw at different initial C/N ratios. Error bars represent standard deviation. (a) NH₄ ⁺-N; (b) NO₃ ⁻-N.

Figure 4. CEC changes during composting of sewage sludge and maize straw at different initial C/N ratios. Error bars represent standard deviation.

Figure 5. TOC changes during composting of sewage sludge and maize straw at different initial C/N ratios. Error bars represent standard deviation.

Figure 6. MC changes during composting of sewage sludge and maize straw at different initial C/N ratios. Error bars represent standard deviation.

Figure 7. GI changes during composting of sewage sludge and maize straw at different C/N ratios. Error bars represent standard deviation.

Table 2. Main absorption bands in FTIR and their assignments for composting mixture

Wavenumber (cm^−1)	Assignments
3444–3419	O–H stretching, N–H stretching (minor), hydrogen-bonded OH
2930–2920	C–H stretching of alkyl structures
2850	C–H asymmetric, C–H stretch of –CH
1640–1650	Aromatic C=C skeletal vibration, C=O stretching of amide groups (amide I band), C=O of quinone and/or H-bonded conjugated ketones
1540–1547	N–H deformation and C=N stretching of amide (amide II band), aromatic C=C stretching
1420	O–H deformation and C–O stretching of phenolic groups
1043–1034	C–O stretching of polysaccharides or polysaccharide-like substances

Figure 8. FTIR spectra change of composting mixtures at different initial C/N ratios with composting time. (a) C/N ratio of 14; (b) C/N ratio of 20; (c) C/N ratio of 25.