Effect of pH regulated Pre hydrolysis on the Energy Consumption of Mechanical Size Reduction of Vegetable Wastes

Abstract:

Pre hydrolysis of vegetable wastes was conducted with swill at different initial pH equal to 5, 6, 7, 8, and 9, and then the energy consumption of mechanical size reduction of raw and pre hydrolysed vegetable wastes was studied. Experimental results showed that at initial pH equal to 7, 8 and 9, the energy consumptions of vegetable wastes after pre hydrolysis were decreased from the original 0.304 J·g-1(wet basis) to 0.032, 0.025 and 0.027 J·g-1(wet basis), respectively, which declined by up to 90%; while those at initial pH equal to 5 and 6 slightly dropped to 0.200 and 0.219 J·g-1(wet basis). During the 8 h pre hydrolysis at initial pH equal to 6, 7, 8 and 9, the pH and mass concentration of total organic carbon, volatile fatty acids and ammonia nitrogen in the liquid phase as well as the mass fraction of lignocellulose in the solid phase had little variations, indicating that the effect of biotic hydrolysis was not obvious. The swelling and moisture absorbing and the structural change of celluloses under alkaline conditions, which can reduce the strength of lignocellulosic material, might be the main reasons for the decrease of energy consumption for mechanical size reduction.

Key words:vegetable waste; pre hydrolysis; pH; mechanical size reduction; energy consumption