| dc.description.abstract | During the last two decades, Indonesian economic growth focused on industrial development especially agroindustrial sector (Suardana, 2008). As a result, agroindustrial wastewater pollution became serious problem. Organic wastewater with high nutrient content can stimulate uncontrolled microalgae growth (Pustekkom, 2005), whereas discipline control can be very profitable. According to Pirt (1986), microalgae is low level vegetation (5 – 30 2m) with high productivity and efficiency in biofuel producing through photosynthesis. Its productivity in producing triglycerides reached 100 000 L/ha, while oil palm reached only 5 950 L/ha (Kabinawa, 2008). Specific cultivation of microalgae raised feasibility problem particularly in Indonesia. Cultivation of natural microalgae consortium in many agroindustrial wastewater, will be delivered to produce dominant, natural selected microalgae with good ability to survive in such extreme condition. This research was performed to determine the effect of several agroindustrial wastewater as nutrient in microalgae natural consortium cultivation. In addition, application of coagulation/flocculation and centrifugation method for separating/harvesting microalgae was also investigated. In the early stage, preparation was performed to create cultivation vessel based on raceway design, characterization of agroindustrial wastewater (slaughterhouse wastewater/L1, livestock wastewater/L2, and sugar mill wastewater/L3), characterization of microalgae natural consortium from LSI Lake- IPB, and also making of trial cultivation. Next stage, primary cultivation was launched in wastewater medium with circulation, wastewater medium without circulation, and synthetic wastewater medium (in many concentrations of NPK fertilizer, without circulation). In the last stage, separation of consortium after cultivation was carried out with centrifugation, and also coagulation/flocculation with alum and polyaluminium chloride (PAC). Characterization of wastewater showed that L2 contain the highest nitrogen (1 490 mg/L) and potassium (304.70 mg/L) concentration, but orthophosphate concentration (8.0 mg/L) lower than L1 (14.8 mg/L). Meanwhile L3 had nitrogen (0 mg/L), orthophosphate (0.6 mg/L), and potassium (107.70 mg/L) concentration at the lowest. Microalgae consortium cell density attained 2 250 000 cell/ml, and its prevalence showed that there are three species of chlorophyceae in large amount, Selenastrum sp., Ankistrodesmus sp., and Dictyosphaerium sp.. Uncounted species in consortium assumed to be in very small amount. Cultivation in wastewater medium with circulation showed that complete microalgae growth phase occurred in 20 – 30 days. During the phase, nutrients such as N, NO3 -, PO4 3-, and K decreased, however, fluctuation occurred (especially NO3 - and PO4 3-) by the perpetual conversion activity which related to food chain between microalgae and the other contaminant microorganisms. Its pH value ranging in proper microalgae growth pH from 7 to 9 but tend to be 8. Drastic color change according to chlorophyceae growth was not appeared due to effect of circulation on the chlorophyll amount. Next cultivation was carried out without circulation in wastewater medium. During 16 days cultivation, complete growth phase was well-detected. NO3 -, PO4 3-, and K concentration also showed decreasing trend, while pH value ranging from 6 to 9 but also tend to be 8. Cultivation in synthetic wastewater medium, consist of 9 serial concentrations of NPK fertilizer (Sy1 – Sy9), was run to prove that nutrient concentration affect the growth rate of microalgae. As a result, the growth peak of Sy3 culture (3 703.70 mg NPK/L) according to the cell density at the 6th day constituted the highest. Its cell density (13 000 000 cell/ml), color (b* value = 12 400), and TSS concentration (315.5 mg/L), higher than the other serial culture. The higher concentration of NPK, the lower growth and color change of microalgae. According to the highest TSS achieved in this culture, microalgae consortium biomass productivity reach 57 579 kg/ha/year. The rate of 20% oil content of microalgae consortium in this culture was checked, lead to 11 516 L/ha/year of oil productivity. This result better than oil productivity from the other crop. The prevalence analysis of microalgae at growth peak in L1 culture without circulation (18 245 000 ind/ml) and also Sy3 synthetic culture (2 630 000 ind/ml) showed that Chlorella sp. dominate both cultures. This point indicate that Chlorella sp. was naturally selected in L1 as well as in Sy3. Microalgae consortium separation with centrifugation (3 800 rpm) showed at optimum in 16 minutes, which TSS removal reach 93%, turbidity removal reach 81%, and color removal reach only 19%. Separation with coagulation/flocculation using alum showed at optimum in 500 mg/L dose, which TSS removal reach 100%, turbidity removal reach 99%, and color removal reach 93%. Meanwhile, the same method using PAC showed at optimum in 250 mg/L dose, which TSS removal reach 96%, turbidity removal reach 99%, and color removal reach 94%. Considering removal efficiency in both method, the most effective one is coagulation/flocculation using alum. | en |
