The Biogas Slurry Hydroponic System

With the development of large-scale livestock breeding and biogas technology, a large amount of biogas slurry is produced in Chinese suburban and rural farms. How to treat the biogas slurry is a difficult problem. Bio-floating islands can not only purify the sewage, but also make full use of nutrients in the biogas slurry. Meanwhile it can ease the problem of insufficient agricultural land. It provides a new idea for the biogas slurry disposal.In this study, the experiment includes the laboratory test and outdoor test. Ipomoea aquatic and celery were planted in biogas slurry separately in summer and winter. The growth of the hydroponic vegetables, the nitrogen and phosphorus and heavy metals removal rate in the biogas slurry, and the nutrients distribution in vegetables are analysed in this paper. The main results are as follows:(1) The laboratory test of hydroponic celery in biogas slurry showed that:the hydroponic celeries planted in the lower-concentration biogas slurry were short but with thick roots; the roots of the celeries planted in the higher-concentration biogas slurry were rotten and the leaves were yellow. With the decrease of the biogas slurry concentration, the biomass growth of the hydroponic celeries increased first and then decreased. The weight ratio of the celery’s above-water and under-water part shows the decreased trend. And the N mass fraction (fresh weight) in the celery’s above-water and under-water part also decreased. But the mass fraction of P did not show any regularity.After80days’hydroponic culture, The TN removal efficiency of celery planted in the biogas slurry diluted100times was the biggest, followed by the biogas slurry diluted50times,40times,30times and20times, and the least was the biogas slurry diluted5times. The TP removal efficiency of celery planted in the biogas slurry diluted10times was the biggest, followed by the biogas slurry diluted20times,40times,50times and30times, and the least was the biogas slurry diluted200times.(2) The laboratory test of hydroponic Ipomoea aquatic in biogas slurry showed that:the survival rate of the hydroponic Ipomoea aquatic in the biogas slurry diluted20times and30times were100%. After40days’hydroponic culture, the biomass growth of hydroponic Ipomoea aquatic in biogas slurry diluted20times and30times were2.75kg (fresh weight)/ m" and2.52kg (fresh weight)/m2. Pb, Cd and Cu were not detected in the biogas slurry diluted20times and30times. The removal efficiency of Zn in the biogas slurry diluted20times was80.2%, and that of the biogas slurry diluted30times was72.1%.(3) The outdoor test of hydroponic Ipomoea aquatic in biogas slurry showed that:at the end of the hydroponic culture, Pb was detected both in the hydroponic water and the Ipomoea aquatic, and the main was in the hydroponic water. Cd was just detected in the hydroponic Ipomoea aquatic. Cu was detected both in the hydroponic water and the sediment, and the main was in the sediment. Zn was detected both in the sediment and hydroponic Ipomoea aquatic, and mainly in the sediment. Pb, Cd and Zn were absorbed by Ipomoea aquatic from the biogas slurry. The uptake of Zn was the greatest, at6.23mg/m2. The uptake of Cd was the smallest, at0.04mg/m2, and that of Pb was0.32mg/m2.(4) In the outdoor test of hydroponic Ipomoea aquatic in biogas slurry, the amount of the heavy metals in the Ipomoea aquatic did not exceed the Chinese standards of green vegetables and safety requirement of environmentally harmless vegetables.