Degradation of solid and muddy organic matter of blue mussels by Bacillus sp

Abstract

Organic matter contained in 4,000 kg of blue mussels was subjected to microbial degradation. Seawater (1,280 liter) trapped in the shells discharged by smashing shells, and the value of chemical oxygen demand (COD) was 5,800 mg/liter. The remaining solid organic matter (2,720 kg) including broken shells was washed with 6,000 liter of tap water to reduce NaCl concentration. The COD in the wastewater was 550 mg/liter. The washed solid organic matter was subjected to compression treatment by using the Screw-press machine to adjust its water content (around 30%) to that optimal for microbial activity, thereby removing 680 liter (COD=11,800 mg/liter) of wastewater from solid organic substances. Wastewater obtained at each process was collected together in one pot, and flocculating agents were added there to cause aggregation and precipitation, thereby recovering organic matter in the form of sludge. Water content of sludge after the belt press process was reduced from 56% to 39%, by vacuum drying. The solid organic matter obtained after washing and compressing and the sludge after vacuum drying were subjected to the degradation (45 h) by Bacillus sp. As a result, 41% (w/w) of the solid organic matter and 20% (w/w) of sludge disappeared. Total carbon and nitrogen ratios were reduced from 6.0 to 5.1 in the solid organic matter and from 12.8 to 12.5 in the sludge, respectively. The concentrations of contaminated heavy metals such as As, Cd, Hg, Ni, Cr, and Pb in the solid organic matter and the sludge were quite less than those of their tolerance levels.