As part of an effort to lower the cost of urease enzyme used in enzyme induced carbonate precipitation (EICP) for soil improvement, urease enzyme was extracted from watermelon seeds. EICP is a biologically-based ground improvement technique in which a solution containing calcium, urea, and urease enzyme is used to induce calcium carbonate precipitation in a granular soil, enhancing strength, and stiffness. To reduce the enzyme cost by obtaining it from a waste material, the effectiveness of urease enzyme extracted from watermelon seeds, a urease-rich agricultural waste, was evaluated. Low-tech methods were employed for extraction and purification of the enzyme. The extracted enzyme, which showed urease activity of around 611 U/ml, was used to treat Ottawa 20/30 sand. Results of scanning electron microscope imaging and energy dispersive X-ray analysis demonstrated calcium carbonate precipitation. The ratio of the precipitated carbonate content to the theoretical maximum was found to be around 64%.

The stability (longevity of activity) of three crude urease extracts was evaluated in a laboratory study as part of an effort to reduce the cost of urease for applications that do not require high purity enzyme. A low-cost, stable source of urease will greatly facilitate engineering applications of urease such as biocementation of soil. Inexpensive crude extracts of urease have been shown to be effective at hydrolyzing urea for carbonate precipitation. However, some studies have suggested that the activity of a crude extract may decrease with time, limiting the potential for its mass production for commercial applications. The stability of crude urease extracts shown to be effective for biocementation was studied. The crude extracts were obtained from jack beans via a simple extraction process, stored at room temperature and at 4 ℃, and periodically tested to evaluate their stability. To facilitate storage and transportation of the extracted enzyme, the longevity of the enzyme following freeze drying (lyophilization) to reduce the crude extract to a powder and subsequent re-hydration into an aqueous solution was evaluated. In an attempt to improve the shelf life of the lyophilized extract, dextran and sucrose were added during lyophilization. The stability of purified commercial urease following rehydration was also investigated. Results of the laboratory tests showed that the lyophilized crude extract maintained its activity during storage more effectively than either the crude extract solution or the rehydrated commercial urease. While incorporating 2% dextran (w/v) prior to lyophilization of the crude extract increased the overall enzymatic activity, it did not enhance the stability of the urease during storage.