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This waste water treatment plant (WWTP) was designed and built to treat the waste water coming from the sting rays leather tannery in Labuan Maringgai, Lampung Selatan. By treating this kind of waste water coming from the sting rays leather tannery, it will decrease the environmental pollution. The product capacity of this tannery was 400 pieces per month and the weight of it was 120 kg. Those skins were tanned into two steps, the number of skins in each process was 200 pieces or 60 kg during 2 weeks. The volume of waste water discharged varied from 1,5 to 5 m3 during 3 days in the beginning of beam house operation or 0.5 to 1 m3per day during the first step of process. The pollution content of such waste water was as follows: COD: 1205,66 - 1400 mg/l; BOD 550 – 950 mg/l; S : 28,9 – 213 mg/l, TSS: 55,16 – 775 mg/l; N-NH3 : 30,18 – 129,6 mg/l; fat/oil : 21 – 292. mg/l; total Cr: 0,47 – 0,76 mg/l; and pH: 9 – 12 respectively. The work hours in operating the WWTP was 5 hours per day, and the debit of it ranged from 0.5 to 1 m3 per hour. The WWTP was designed for the max COD of 1.500 mg/l and BOD 750 mg/l. The system of WWTP was pre treatment, homogenization, flocculation and coagulation, 1st anaerobic facultative and 2nd anaerobic facultative, sludge drying bed and final control tank. The efficiency of this WWTP ranged from 22,53 to 97%.

Leather tanning waste water contains chemical compounds, such as chromium and NH4+ in high concentration, so if they are thrown away without treatment they will make some problems. The aims of this research is to adsorb the cations in leather tanning waste water i.e chromium and NH4+ used natural zeolite as an adsorbent. Research was done by comparing amount of chromium and NH4+ in effluent waste water treatment unit with amount of chromium and NH4+ after being adsorbed by zeolite in a batch system. The result of this research showed that efficiency difference between using zeolite and waste water treatment unit was significant. The optimal condition to reduce chromium and NH4+ was by using 300 grams per liter waste, zeolite particle size was 50-60 mesh, contact time was 24 hours and pH 8±0,1. In this condition, zeolites could reduce chromium from 3728,56mg/l to 365,39 mg/l or 90,20%, and NH4+ from 3040,02 mg/l menjadi 209,76 mg/l or 93,10%. Waste water treatment unit could reduce chromium 63,55% and NH4+ 56,75%.

Stingray fish potential in Indonesia is big enough but has not yet been exploited maximally, only some area like Lampung which is already exploiting the stingray leather tanning them and sell to Java. From the result of the research, stringray leather could pieces the big enough advantage that was at the price of selling Rp. 68.000,- per pieces pay back periode in average, would obtain the advange before the tax Rp. 285.649.697,- peryear and the advantage after the tax Rp. 228.519.757,- per year, pay back periode before the tax was in 1 year and 10 months and back periode after the tax was in 2 years and 2 month. As for break event point 35.04% with the value Rp. 978.385.533,- with break event value point capacitie production 14.388 pieces per year. Based on the result of the calculation of investments criteria was NPV (net present value) = Rp. 162.570.834,- (greater tan zero) while IRR = 30,54% greater than SOCC (DF = 18%) from the pay back periode = 2 year 1 month. Therefore from the market analysis and the production aspect, the effect of leather industry of stingray fish is so feasible that is competent to be developed in some areas having big potential stingray fish in Indonesia, so that it can improve the working opportunity and the effort for all of fishermen and their family.