Production, characterization, and evaluation of two types of slow-releasing carbon source tablets for in-situ heterotrophic nitrate denitrification in aquifers

Slow-releasing carbon source tablets were manufactured for an in-situ biological denitrification system. The average zero-order nitrate degradation rates seen, from highest to lowest, were in microcosms to which lactate, fumarate, propionate, and formate had been added. Fumarate was approximately 80% cheaper than lactate, and consequently was determined to be the most optimal slow-releasing carbon source in tablet form. The slow-releasing precipitating tablet (SRPT) and slow-releasing floating tablet (SRFT) were manufactured with hydroxypropyl methylcellulose (HPMC) as the agent of release control, microcrystalline cellulose pH 101 (MCC 101) as the binder, #8 sand as the precipitation agent, and calcium carbonate and citric acid as floating agents. Fourier transform infrared spectroscopy and powder X-ray diffraction indicated that the crystal arrangement in the SRPTs and SRFTs was maintained and ordered in a manner similar to raw excipients. SRFTs floated in water within 30 min and remained so for 5 d due to the buoyancy of carbon dioxide. The carbon source release rate was proportional to the quantity of HPMC added. The longevities of SRPT with 300 mg of HPMC and SRFT with 400 mg of HPMC were 25.4 d and 37.3 d, respectively. This study observed that SRPT and SRFT were manufactured effectively and are suitable for in-situ slow-releasing biological systems.