Chiang Mai Journal of Science

Many agro-industries in Thailand discharge untreated wastewater with high organic content causing severe environmental problems. The objectives of  this study were to provide a wastewater treatment system for a fermented fish production factory and to demonstrate the constructed wetland technology as an on-site solution for the treatment of  wastewater which is economical, and not complicated to operate or maintain. The wastewater from fermented fish production contains BOD, COD, TKN, grease and oil at approximately 6,200, 9,770, 540 and 660 mg/L, respectively. Pre-treatment by a grease trap and an anaerobic process is required prior to two constructed wetland beds connected in series. The first bed is a subsurface horizontal flow bed (180 m²) filled with stone (1-2 inch) and planted with Umbrella sedge (Cyperus flabelliformis Rottb ). The second bed is a free water surface bed (140 m²) planted with Canna (Canna hybrida). The designed capacity of the treatment system is 10 m³/d though presently the maximum volume of wastewater received daily is only 5-7 m³ The factory . operates around 5 days per week and 4 hours per day on average depending on the amount of  fish processed.  A grease trap and a UASB reactor reduce grease and oil, BOD and COD efficiently but only 50% for TKN was eventually reduced in the two wetland beds.  The overall removal efficiencies of  the system were over 97% for COD, BOD, SS and grease and oil and was around 70% for TKN and NH₄+-N. Wastewater from the free water surface bed was reused for gardening