Nutrient export and material recycling using aquatic plants: Lake Kitagata case study

Abstract

Lake Kitagata in Fukui Prefecture, Japan, was examined to collect fundamental data on nutrient export and material recycling using the native aquatic plants, common reed and wild rice. Common reed was located all over the lake shore, while wild rice was in the upper part of the lake. On average, the nutrient content was nitrogen: 2.1 and 2.6 %, P2O5: 0.38 and 0.64 %, K2O: 2.1 and 2.4 % for common reed and wild rice, respectively, and decreased along with their growth. If harvested in October, the nitrogen and phosphorus exported from the lake were estimated to be only 1.1 and 1.9 % of the inflow, respectively. Methane fermentation of these plants showed an average of 134 and 150 mL-CH4/g-VS added for common reed and wild rice, respectively, indicating possible use as an auxiliary source. The composting of these plants mixed with chicken manure, bean curd and rice bran was successful, and the products were rich in the major nutrients and well-balanced. A pretreatment method combining sulfuric acid and thermal treatment was able to convert about 50 % of cellulose in common reed to glucose, the precursor for bioethanol production. Therefore, these technologies are demonstrated to be helpful for the beneficial use of the biomass.