冬季水库水源中MIB和土嗅素的产生与降解机理

2-甲基异冰片(MIB) 和土嗅素(geosmin)由放线菌,真菌和蓝绿藻代谢产生,这两种物质是目前造成饮用水具有霉味和土味的主要原因.以包头市画匠水库为研究对象,运用推流式反应器基本模型和OriginPro 9.0线性拟合法,分析冬季水源水库水中MIB和土嗅素净产率与损失率;运用双膜理论计算嗅味物质挥发速率常数.结果表明,冬季画匠水库0.55m冰层下,透射光照强度(Surface PAR)为70 ~ 636W/m2,平均光照强度为114.8W/m2,存在合适藻类代谢产生异味物质的光照条件.封冻前后,水库水中MIB和土嗅素浓度逐渐增高,并以60~102ng/L的较高浓度水平维持到来年解冻,此后二者浓度逐渐降低到较低水平,呈规律性变化.曲线拟合结果显示,冬季画匠水库水中MIB/土嗅素的产生与减少均符合准一级反应动力学模型(R2为0.941~0.989).由于低温与冰层阻碍等原因,影响水库中MIB/土嗅素的损失主要因素是出流携带;冰层融化后,挥发和出流携带是MIB/土嗅素减少的主要原因.MIB和土嗅素冬季产生速率常数为4.119, 2.146ng/(L×d),水流携带损失速率常数为0.032d-1.冰层融化后,MIB产生速率为1.012ng/(L×d),损失速率为0.072d-1,藻细胞产率4.57×10-8ng/(L×d×cell);土嗅素产生速率常数为1.638ng/(L×d),损失速率为0.083d-1,藻细胞产率5.46×10-8ng/(L×d×cell).

Occurrence and degradation of 2-methylisoborneol and geosmin in water supply reservoir in winter

The production of 2-MIB and geosmin by actinomycetes and cyanobacteria are causes of many musty/earthy odor complaints about the aesthetics of drinking water. These two compounds are noticeable at nanograms per liter levels, and for the lower TON, tastes and odours (T&O) are always ranked as one of the first three causes of complaints in developed countries. This study evaluated a water supply reservoir with bottom-release (hypolimnion) outlet structure in Baotou city. According to the plug flow reactor model, mass balance analyses on T&O compounds in the reservoir were used to calculate in situ field rates of net MIB and geosmin production and loss. Taste and odor compounds loss rates caused by volatilization was calculated from two-film theory. Experimental results indicated that under the ice which the thickness was 0.55m, and the surface photosynthetically active radiation (PAR) varied from 70to 636W/m2from November to March of next year. The average surface PAR was 114.8W/m2, and the lowest value was 70.57W/m2 (in December). The surface PAR in Huajiang reservoir satisfied the growth and geosmin production of the algae in winter. MIB/geosmin concentrations in the reservoir followed the same seasonal trend as concentrations increasing and decreasing according to ice freeze and melt. The loss rates followed a first-order relationship for all cases tested (R2ranged from 0.941to 0.989), with volatilization and outlet fluid carrying being the key mechanisms during the lower temperature period. Mass balance analyses on MIB/geosmin during ice freezing indicated that the rate of MIB/geosmin production was 4.119 and 2.146ng/(L×d), MIB/geosmin emission rate constant was 0.032d-1all due to outlet fluid carrying. During ice melting, MIB/geosmin production was 1.012, 1.638ng/(L×d), MIB/geosmin emission rate constant was 0.072, 0.083d-1caused by volatilization and outlet fluid carrying. Volatilization appeared more important than biodegradation, photolysis or adsorption in Huajiang reservoir in winter.