Isnin, 4 Mei 2009

Wheat Straw can be used as biofilter media / Aquacultural Engineering (2007) 37, 222-233

Soares and Abeliovich (1998) and Aslan and Turkman(2003) indicate that wheat straw can be used as biofilter media and as a carbon source for the denitrification of drinking water. Lowengart et al. (1993) also used wheat straw to denitrify turbid and nitrogen-rich irrigation water. Similarly, Blowes et al. (1994) have demonstrated that wood chips can be used to as a biofilter media to treat runoff and irrigation water. Kim et al.(2003) investigated the use of both wood chips and wheat straw for nitrate removal in a bioretention study. Robertson et al. (2000) have evaluated sawdust, leafcompost, unprocessed grain seeds and wood mulch as reactive barriers to the flow of nitrate-laden waters. More recently, Robertson et al. (2005) reported on a commercially available wood-based biofilter media (marketed as NitrexTM) to remove nitrate–nitrogen froma pretreated residential septic tank effluent. Volokitaet al. (1996) studied shredded newspaper as a biofilter media in denitrification columns.

Study evaluated wood chips and wheat straw as inexpensive and readily available alternatives to more expensive plasticmedia for denitrification processes in treating aquaculture wastewaters or other high nitrate waters. Nine 3.8-L laboratory scale reactors (40 cm packed height  10 cm diameter) were used to compare the performance of wood chips, wheat straw, and Kaldnes plastic media in the removal of nitrate from synthetic aquaculture wastewater. These upflow bioreactors were loaded at a constant flow rate and three influent NO3–N concentrations of 50, 120, and 200 mg/L each for at least 4 weeks, in sequence. These experiments showed that both wood chips and wheat straw produced comparable denitrification rates to the Kaldnes plastic media. As much as 99% of nitrate was removed from the wastewater of 200 mg NO3–N/L influent concentration. Pseudo-steady state denitrification rates for 200 mg NO3–N/L influent concentrations averaged (1360 Æ 40) g N/(m3 d) for wood chips,(1360 Æ 80) g N/(m3 d) for wheat straw, and (1330 Æ 70) g N/(m3 d) for Kaldnes media. These values were not the maximumpotential of the reactors as nitrate profiles up through the reactors indicated that nitrate reductions in the lower half of the reactors were more than double the averages for the whole reactor. COD consumption per unit of NO3–N removed was highest with the Kaldnes media (3.41–3.95) compared to wood chips (3.34–3.64) and wheat straw (3.26–3.46). Effluent ammonia concentrations were near zero while nitrites were around 2.0 mg NO2–N/L for all reactor types and loading rates. During the denitrification process, alkalinity and pH increased while the oxidation–reduction potential decreased with nitrate removal. Wood chips and wheat straw lost 16.2% and 37.7% of their masses, respectively, during the 140-day experiment. There were signs of physical degradation that included discoloration and structural transformation. The carbon to nitrogen ratio of the mediaalso decreased. Both wood chips and wheat straw can be used as filter media for biological denitrification, but time limitations forthe life of both materials must be considered.

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