This literature review surveys the previous and current researches on the co-digestion of anaerobic processes and examines the synergies effect of co-digestion with cattle manure. Furthermore, this review also pays attention to different operational conditions like operating temperature, organic loading rate (OLR), hydraulic retention time (HRT), chemical oxygen demand (COD) and volatile solid (VS) removal efficiency and biogas or methane production. This review shows that anaerobic mono-digestion of cattle manure usually causing poor performance and stability. Anaerobic studies were generally performed under mesophilic conditions maintained between 35 and 37°C. Organic waste loading rate generally ranges from 1 to 6 g VS-COD L -1 day -1 stable condition in anaerobic digester. Generally, studies show that HRT for co-digestion of fruit-vegetables waste and industrial organic waste appears to exceed 20 days. However, the anaerobic co-digestion process is generally operated at HRT of between 10 and 20 days. VS and COD removal efficiency usually reaches up to 90 % due to codigestion with different type organic waste. Methane-biogas production is generally obtained between 0.1 and 0.65 L CH 4 -biogas g -1 VS.

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The improvement of water quality parameters by wetland systems is an increasingly global practice. In the present study, the utilization of a treatment method comprising of an upflow anaerobic sludge blanket (UASB) reactor followed by a surface flow (SF) and a vertical flow (VF) wetland (hybrid wetland) in the arrangement has been tested experimentally. Lemna minor was used in wetland units at a planting density about 3 kg wet m. The UASB reactor effluents were diluted with tap water to keep the influent chemical oxygen demand (COD) at about 1000 mg L and then fed semi-continuously to lab-scale hybrid wetland system. Removal efficiency ranged from 80 to 93% treatment for COD and biochemical oxygen demand (BOD), about 92-98% for total phosphorus (TP) treatment and total Kjeldahl nitrogen (TKN), and except Hg (approximately 83%), heavy metal removal was over 90%. Post-treatment of UASB reactor effluents with hybrid wetland provided a high COD, BOD, TKN, ammonia-nitrogen, TP and phosphate-phosphorus removal and efficiently removed heavy metals (Hg, Cr, Zn, Al, As, Cd, Co, Cu, Pb and Ni). In addition to this, the bioconcentration factor of these heavy metals by the L. minor was also studied in the present study.

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