Sand Quality Improvement Using Watermelon (Citrullus Lanatus) Seeds -Derived UreaseInduced Calcium Carbonate Precipitation

Abstract

In Pakistan, the global warming and liquefaction problems have increased due to CO2 emissions during the
cement manufacturing process and the water absorption ability of the cement, respectively. Recently, enzyme-induced
carbonate precipitation (EICP) has become increasingly popular due to its eco-friendly nature and mechanical properties.
This study is aimed to extract the crude urease enzyme from watermelon seeds, considered "food waste," to test its effects
on biocementation and produce a building material with more strength and less permeability for water absorption.
Watermelon seeds were used in dry and germinated conditions to investigate urease activity and calcium carbonate
formation. The EICP-coated brick showed less weight change than the control brick. The bricks were added in cycles (1,
7, 14 times); the 14-cycle brick was firmer than the other two bricks, but still wasn't sufficiently durable. Therefore to
overcome this problem, another EICP method was used, which is the one-phase method, in which a large volume of EICP
solution was mixed with sand in the same brick, and compacted in a mold again. The brick was incubated at 35–37 ˚C
and cured for 14 days, resulting in a hardened brick. A water absorption test was conducted on the sample, and it was
found that the bio brick could not endure the water conditions for a long period of time. Scanning Electron Microscopy
(SEM) confirmed that major vaterites were formed instead of calcite, which was the cause of some disintegration of the
bio brick. However, it is suggested that the EICP solution can be used as a binder in crack-filling.