Sludge management is one of the most difficult and expensive problems in
wastewater treatment plant operation. Consequently, & / #8216 / sludge minimization& / #8217 / concept
arose to solve the excess sludge production by sludge pretreatment.
Sludge pretreatment converts the waste sludge into a more bioavailable substrate
for anaerobic digestion and leads to an enhanced degradation. The enhanced degradation
results in more organic reduction and more biogas production. Therefore, sludge
pretreatment is a means of improving sludge management in a treatment plant.
Among pretreatment methods, acidic pretreatment has been subject of limited
successful studies reported in the literature. On the contrary / ultrasonic pretreatment was
reported as an effective pretreatment method. Main objective of this study was to investigate the effects of these two pretreatment methods and their combination in order
to achieve a synergistic effect and improve the success of both pretreatment methods.
Experimental investigation of pretreatment methods consists of preliminary
studies for deciding the most appropriate pretreatment method. Anaerobic batch tests
were conducted for optimization of the parameters of selected method. Finally, operation
of semi-continuous anaerobic reactors was to investigate the effect of pretreatment on
anaerobic digestion in details.
Preliminary studies indicated that, more effective pretreatment method in terms
of solubilization of organics is ultrasonic pretreatment. Fifteen minutes of sonication
enhanced 50 mg/L initial soluble COD concentration up to a value of 2500 mg/L.
Biochemical methane potential tests indicated that the increased soluble substrate
improved anaerobic biodegradability concurrently. Finally, semi-continuous anaerobic
reactors were used to investigate the efficiency of pretreatment under different operating
conditions.
Results indicate that at SRT 15 days and OLR 0.5 kg/m3d ultrasonic pretreatment
improved the daily biogas production of anaerobic digester by 49% and methane
percentage by 16% and 24% more volatile solids were removed after pretreatment.
Moreover, even after pushing reactors into worse operating conditions such as shorter
solids retention time (7.5 days) and low strength influent, pretreatment worked
efficiently and improved the anaerobic digestion.
Finally cost calculations were performed. Considering the gatherings from
enhancement of biogas amount, higher methane percentage and smaller amounts of
volatile solid disposal from a treatment plant / installation and operation costs of
ultrasound were calculated. The payback period of the installation was found to be 4.7
years.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12610366/index.pdf |
| Date | 01 February 2009 |
| Creators | Apul, Onur Guven |
| Contributors | Sanin, Dilek Faika |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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