Two hundred forty thousand (240,000) tons of coffee waste and about 4000 tons ofrnflower residue wastes are generated annually from the age-old coffee processingrnindustries and the booming cut flower industries in Ethiopia, respectively. Most of thesernwastes are released to the environment without treatment, and their direct release pollutesrnthe environment, mainly inhibiting plant growth. This necessitates the transformation ofrnthese wastes into beneficial products with a dual purpose of production of bio fertilizerrnand protection of the environment. To this end, a study was made to evaluate the processrnof composting of coffee husks and flower residues separately in order to determine theirrncompost quality. Each material was arranged in to three different piles in a trapezoidalrnWindrow composting for 90 days and more, and monitored for their physico-chemical,rnmicrobiological and phyto-toxicological properties during the whole process.rnCoffee husk (CH) amended with cow dung plus house hold compost (CHCD: Pile 1) andrnwith fruit/vegetable wastes plus house hold compost (CHFVW: Pile 2) were arranged andrncompared against the control (CH: Pile 3) without any amendment. As a result, the twornamended treatments showed similar pattern of temperature profile with the firstrnmesophilic stage (18-42oC) in the first 2 days followed by the thermophilic stage (45-rn70oC) up to 45 days, and declined to the second mesophilic stage afterwards andrnremained so until the end of the experiment. In all cases, there was a steady decline ofrnmoisture content (MC %), reduction in total organic carbon (TOC%) and a rise in totalrnNitrogen (TN%) because of the loss of carbon in the form of CO2 thereby decreasing thernC:N ratio of Pile 1, Pile 2, and Pile 3 to 11, 13, and 18, respectively. The highest bacterialrncount of 9.78logMPN g-1dw (Pile1) and 9.45logMPN g-1 dw (Pile 2) was seen at the start of the process; while the highest actinobacterial counts of 9.78logMPNdw (Pile 1 and Pile 2)rnand fungal counts of 9.78log MPN g-1 dw (Pile 1) and 9.45 MPN g-1 dw (Pile 3) werernrecorded at the end of the composting process, respectively. This change in numberrnindicated a clear microbial succession along the process. The effect of the differentrnmicrobial activities was reflected in the better maturation of Pile 1 with a GerminationrnIndex value >80% and C/N ratio of 11 at the end of composting compared to the controlrnthat required much more days for the material to become free from phytotoxicity. Thisrntransformation could be associated with higher volatile solid reduction (75% in Pile 1 andrn65% in Pile 2), substantiating the importance of chemical parameters in coffee huskrncompost.rnThe same feed stock was also composted with cow dung (Pile 1), with fruit/vegetablernwastes (Pile 2) and coffee husk alone (Pile 3) again to study their microbial diversity andrnenzyme activities; and samples were collected on days 0, 32 and 90. Similar changes inrnTOC (%) and in TN(%) were found resulting in lower C/N ratios of 11 and 13 for Pile 1rnand Pile 2, respectively due to changes in temperature profile, pH and water content ofrnthe mixture. This change which directed the succession of different microbial groups wasrnaccompanied by the release of compost relevant enzymes: hydrolases, phosphatases,rnpeptidases and proteases in Pile 1 and Pile 2 at the start; and esterase at the end of thernprocess.rnFurthermore, denaturing gradient gel electrophoresis (DGGE) analysis of coffee huskrncomposting indicated distinctive community shifts during the composting process. ThernDGGE revealed that bacterial and fungal communities of samples from day 0 werernclustered separately from communities of samples from day 32 and 90, indicating a change in the bacterial and fungal community composition. This result attributed thatrnmicrobial communities at the start were responsible in the degradation of labile organicrnsubstrates while those communities at the end involved in the stabilization of the process.rnYoung compost of Pile 1 and 2 were clustered separately from Pile 3 as the two cosubstratesrnintroduced different and diverse microbial communities into the compostingrnprocess. On the contrary, microbial community in the matured compost was groupedrntogether showing the end compost were homogenous with well-defined microbialrncommunities.rnPrincipal Component Analysis (PCA) of compost communities from day 0 and day 90rncomposts analyzed by COMPOCHIP microarray explained 62.5% of the variations. As arnresult, probes KO443 and 444 (Stenotrophomonas maltophilia), KO609, KO610 andrnKO614 (Brevundimonas/Caulobacter), KO500 (Derxia gummosa) KO612, 615, 616 andrn617 (Flavobacterium/Flexibacter), KO541 (Pseudomonas putida), KO252rn(Acinetobacter) and KO342 (Actinomyces sp.) were found to be more influential inrndiscriminating the samples into different composting phases. Besides, Brevundimonas,rnCaulobacter, Chryseobacterium Sphingobacterium were dominant during the firstrnmesophilic phase in Piles 1 and 2. These species have broader degradation activity ofrncomplex biopolymers. On the other hand, Flavobacteria/Flexibacter was detectedrnsignificantly in all samples, suggesting their importance in the composting process. Inrngeneral, microbial diversity and numbers were lower in the mature composts as indicatedrnby DELTA 495a, Alpha proteobacteria and Low G+C,rnXylella/Xanthomonas/Stenotrophomonas (KO241), Azotobacter beijerinckii (KO277) and the Actinomyces (KO342). Especially, the presence of Actinomycetes was an indicator ofrnmature compost.rnIn flower residue, the major feed stock (flower residue) was blended with cow dung (Pilern1), with activated EM (Effective Microorganisms) and molasses (Pile 2) and comparedrnagainst the control (Pile 3) without any amendment for the same period of compostingrnand the same composting system. Changes in NH4-N, NO3-N, NH4:NO3 ratio, available Prnand K and concentration of micronutrients (Cu, Zn, Fe, Mn) were included in thernchemical analysis in addition to TOC%, TN% and C/N ratio to better understand thernefficiency of chemical parameters in maturity indices.rnConsequently, the reduction in TOC (%) and the steady increase in TN(%) resulted inrn10%, 16% and 24% of C/N ratios at the end of the process for Pile 1, Pile 2 and Pile 3,rnrespectively. The use of inorganic N forms (NH4-N, NO3-N and NH4-N to NO3-N ratios)rnas indicators of maturity showed significant differences among the three piles. WhilernNH4-N reduced below 400 mg/kg in all piles which was the maximum threshold level forrnmatured compost, NO3-N showed an increasing trend, resulting in lower NH4-N to NO3-rnN ratio (0.12) of Pile 1, compared to Pile 2 and Pile 3 which could not reduce below 0.38rnand 0.58, respectively. The analysis of available P and K also showed an increasing trendrnin all piles, but the concentration of available P (0.7-1%) at the end of the process wasrnsufficient for soil nutrient supplementation. On the contrary, available K and allrnmicronutrients were below the sufficiency level for plant production.rnIn general, the effect of the different microbial activities was reflected in the betterrnmaturation of Pile 1, showing a low C/N ratio (10-11) and high GI% (80-85%) at the end of the composting; and significantly correlated with temperature, water content, pH overrnthe 90 days of composting of both coffee husk and flower residue composts.rnComparatively, Pile 2 and control of both the composting processes required more daysrnfor maturity in this respect.rnIn conclusion, a polyphasic approach using physico-chemical and biological parametersrnincluding temperature, C/N ratio, GI%, NH4:NO3 ratio, enzyme assay together withrnmolecular tools are very essential to evaluate maturity and stability of coffee husk andrnflower residue composts. Bulking agents that have much amendment potential like cowrndung must be encouraged in large scale composting industries to tackle the currentrnenvironmental challenges; and further studies on composting of various sources of solidrnorganic wastes with a different composting system can offer greater insight on thernquality, safety and age of composting. The nutritional and economic feasibility of theserncompost products must be addressed in order to fully realize their benefits and tornunderstand the implication of the end products on plant production.rnKey words/phrases: Coffee husk compost; COMPOCHIP microarray; Enzyme activity;rnOrganic matter degradation; PCR-DGGE; Germination index