Co-digestion of sewage sludges with thermochemically pretreated greenhouse residues

In this thesis, thermal-H2SO4, thermal-HCl, thermal-NaOH and thermal-Ca(OH)2 pretreatment processes were applied to the lignocellulosic greenhouse residues in order to enhance the anaerobic digestion. To enhance co-digestion of sewage sludge, thermochemically pretreated lignocellulosic greenhouse residues were added to sewage sludge with a ratio 20, 40, 50, 60, 80 and 100% by weight to evaluate their methane production potentials with the standart biochemical methane potential (BMP) test. When co-digestion of sewage sludges with raw greenhouse residues were evaluated, removal rate of tCOD is decreased, however VS reduction, methane production and reaction rate constants have been increased by increasing the amount of greenhouse residues in the mixture. The highest methane production value was obtained as 299.40 mLCH4/gVS when the mixing ratio was 20:80. In the co-digestion of sewage sludge with pretreated greenhouse residues by thermal-H2SO4, reaction rate constants and VS reduction rates were decreased with the addition of pretreated samples by thermal-H2SO4 to the sewage sludge. Methane production were also adversely affected. This research revealed that the greenhouse residues which were pretreated by thermal-H2SO4 didn?t enhance the co-digestion of sewage sludge. Another acidic pretreatment process applied on greenhouse residues was thermal-HCl pretreatment. It was detected that the addition of pretreated samples (1.44H and OPT1) by thermal- HCl to the sewage sludge showed no considerable variation in the reaction rate constant. Furthermore, VS reductions, tCOD removal rates and methane production were increased. The highest cumulative methane productions were found as 362.10 mLCH4/gVS and 313.62 mLCH4/gVS from the 20:80 mixing ratio of 1.44H (60°C ? 5% TS - 1.44% HCl - 324 rpm - 1 hour) and OPT1 (60°C ? 5% TS ? 0% HCl - 500 rpm - 1 hour) samples with the sewage sludge, respectively. When co-digestion of sewage sludge with thermal-NaOH pretreated greenhouse residues were evaluated, no significant difference were observed in the reaction rate constants, however VS reductions and tCOD removal rates were increased with the addition of pretreated samples (60N-70N) by thermal-NaOH to the sewage sludge. These increments were positively reflected to methane production. The highest cumulative methane production are 360.44 mLCH4/gVS and 364.19 mLCH4/gVS from the 20:80 mixing ratio of 60N (60°C ? 5% TS ? 0% NaOH ? 0 rpm ? 1 hour) and 70N (70.98°C ? 5% TS ? 0.23% NaOH ? 0 rpm ? 1 hour) samples with the sewage sludge, respectively. When the codigestion of the sewage sludge and the thermal-NaOH preatreated greenhouse residues were evaluated, the optimum mixing ratios were obtained as 40:60 and 20:80. The thermal-Ca(OH)2 pretreatment application was another alkaline pretreatment process applied on greenhouse residues. It was detected that the reaction rate constants were similar by the addition of pretreated samples (0.11K and K4) by thermal- Ca(OH)2 to the sewage sludge. However VS reductions and tCOD removal rates and also methane production were increased. The highest cumulative methane productions were found as 314.78 mLCH4/gVS and 279.62 mLCH4/gVS from the 20:80 mixing ratio of 0.11K (60°C ? 5% TS ? 0.11 gr Ca(OH)2/g waste - 0 rpm ? 1 hour) and K4 (60°C ? 5% TS ? 0 gr Ca(OH)2/g waste ? 233 rpm ? 1 hour) samples with the sewage sludge, respectively. The optimum mixing ratios were obtained as 50:50, 40:60 and 20:80 for co-digestion of sewage sludge and thermal- Ca(OH)2 preatreated greenhouse residues. In this thesis, co-digestion of sewage sludges with greenhouse residues was enhanced when thermochemically (thermal-NaOH, thermal-Ca(OH)2 and thermal- HCl) pretreated samples were used. However, thermal- H2SO4 pretreated greenhouse residues indicated no considerable enhancement in sewage sludge co-digestion. Furthermore, the results indicated that thermal-NaOH pretreatment process is promising since pretreated greenhouse residues significantly increases the methane production, when compared to other thermochemical pretreatment. Co-digestion of sewage sludge with thermochemically pretreated greenhouse residues to increase the biogas production has presented as an alternative process for energy production of organic wastes in Antalya province.KEYWORDS: Sewage sludge, co-digestion, biochemical methane potential, , greenhouse residues, and thermochemical pretreatment