Alemayehu, Esayas (Professor)Chebude, Yonas (Professor)Mekonnen, Andualem (Professor)Dagnew, Getachew2021-09-162023-11-182021-09-162023-11-182021-05-26http://etd.aau.edu.et/handle/12345678/27917In spite of the increasing demand for potable and fuel ethanol, the distillery industries continue to be a major source of surface water and soil pollution, especially to developing nations, due to the release of a highly organic and complex byproduct- the stillage. Stillage contains solids, recalcitrant organics, persistent color, sulfate, chlorides, phosphorus and nitrogen, whose recovery and treatment plays a major role in environmental sustainability. In most cases, the application of single stillage treatment technology did not succeed. The objective of this study was to quantify molasses and stillage byproducts in Ethiopia and examine the feasibility of an integrated treatment approach towards sustainability. Standard methods were applied, beginning from a systematic literature review through primary data collection, stillage sampling and conducting a series of experiments. The trials were set-up based on a sound design followed by standard analytics and a statistical analysis of the results. The experiments started with determining the biochemical methane potential (BMP) test and then undertaking a mild iron oxide coated sand (IOCS) based wet air pretreatment (WAp) through anaerobic digestion (AD), adsorption and a polishing aerobic degradation. From a quantitative characterization study, Ethiopia currently produces close to 1.8 million tons of cane sugar, with the release of over 300,000 tons of molasses as a by-product. Using cane molasses as a raw material and with the release of 431,000 m3 of stillage into the environment, the potable ethanol industry in the country produces over 33,000 m3 of ethanol annually. According to the BMP test run for 45 days at mesophilic condition, molasses stillage has the potential of giving 139 NmlCH4/g-COD with 68% purity. A mild IOCS based WAp of the stillage sample at 3.5% IOCS loading, a temperature of 60 oC, which was held for four hours at atmospheric pressure brought the desirable effect in detoxification. The result observed following comparison of raw and treated stillage from E. coli incubation at 37 oC and 86 revolutions per minute of shaking demonstrated a statistically significant difference (p-value = 0.02) in toxicity. Successively, the consequence of a mild, IOCS based WAp on the methane (biogas) yield as well as the biochemical oxygen demand (BOD) and COD removal was compared with the raw counterpart using batch mesophilic (35±2 oC) AD of stillage. Further, the effect of applying scoria (a highly vesicular igneous rock) support on AD process stability and performance was assessed for the first time. Consequently, a statistically significant (p-value < 0.05) difference in the cumulative specific raw without scoria support, raw with scoria support and WAOp scoria supported stillage AD subsequently. The soluble COD (CODsol) after AD of stillage with scoria, without scoria and with scoria and WAp in mg/l was 30041.7, 30666.7, and 13375.0 respectively. With the WAOp and scoria supported stillage AD a BOD and COD reduction of ≈100% and 92% were achieved. These achievements are unique in stillage recovery and pollution remediation findings so far. Further, the biogas yield with respect to the reaction days (within 18 days) with a relatively stable process (average pH=7.7, 6.8 and 6.7 for pretreated and untreated stillage with scoria and without scoria) was hastened due to pre-treatment. Regarding the adsorption trial on stillage after the batch AD, all the significant COD removals were observed after three hours of contact time for all doses of the treated scoria adsorbent. Maximum removal rate was at 0.03 mg/ml of scoria dosing and in three hours contact time whereby the final COD of the stillage did go lower only to 7500 mg/l. In a related experiment, the effect of organic loading rate (OLR) and stillage WAp was studied in a continuous AD in scoria-packed column reactors. The removal of stillage COD was significantly better (p-value = 0.036), with an average of 13% difference, due to pre-treatment of stillage with an increased OLR to 2000 mg/L-d. In a further polishing aerobic treatment trial of the effluent from the stillage batch AD, a complete removal of the BOD and significant removal of COD, with an average effluent COD of 2278 mg/L was achieved. In fact, 68% of the COD removal occurred within eight hours of digestion. Despite the persistence of color, the removal of organics with bioenergy recovery from integrating the WAp, the batch AD and the aerobic remediations (˜99% COD and 100% BOD removals) of stillage appear to be a promising technique in its sustainable management while adhering to the regulators’ discharge limits.enDistillery StillageWater Pollution ControlIntegrated ApproachEfficient TreatmentRecoveryThesis