A nature inspired approach for producing bio-cements from Urine.

The aim of this work was to produce bio-solids using microbial precipitation and the urea present in human urine. The reason for engaging with such a project was to find an alternative use for urine. Removing nitrogen and phosphorus from a wastewater treatment plant requires large amounts of energy, separating urine and excreta at the source would negate this energy requirement. This work seeks to use urine as an alternative source of urea for bio-brick production in a more energy and water efficient brick-making process. In addition, the urine is sourced from urinals which also stabilize the urine (prevention of urea hydrolysis) while producing calcium phosphate, an inorganic fertilizer. Microbially Induced Calcium Carbonate Precipitation (MICP) was investigated for the production of these bio-solids using synthetic urine and real urine. This was done using the bacteria Sporosarcina Pasteurii. First, the stabilized urine was titrated to investigate its buffer capacity. Thereafter, tests on the effect of the alkalinity of the urine on MICP and ureolytic activity was performed. These tests indicated that real urine could be used as cementation media for MICP provided the pH was decreased to 10.8 or below. Next, ordinary masonry sand was added to customized column reactors. The sand was inoculated with the bacteria and then the cementation media was pumped through the column to fill the pore volume. The media was retained for three hours. Every three hours new cementation media was pumped through the column. The pH of the media was adjusted with 0.1 M HCl to reach a pH of 10.8. Additional calcium was added in the form of calcium chloride to increase the amount of calcium carbonate that could precipitate between the loose sand particles. To fill a pore volume of 12.5% it would theoretically take 8 days with 56 treatments for a column to solidify, assuming the calcium usage efficiency is 85%. To produce bio-solids with the same volume as a standard brick, the following inputs would be required: 1.72 dm3 masonry sand, 36 L of urine, 433 g of calcium chloride dihydrate, 133 mL of 32% HCl and 850 mL of bacteria culture. The process could produce a profit of R24 per brick, provided calcium phosphate and ammonium sulfate are also produced. The proposed integrated system combines the production of bio-solids with waterless urinals and phosphate and ammonia fertilizer production.