Copper mine tailings valorization using microbial induced calcium carbonate precipitation.

The solidification of copper mine tailings was investigated by using the natural biological process known as microbial induced calcium carbonate precipitation (MICP) as a potential method to valorize this waste stream. A submergent method was used to grow bio-columns and the toxicity of copper on Sporosarcina pasteurii (the ureolytic bacteria which drives the MICP process) was investigated. The bio-columns produced from copper mine tailings had a compressive strength of 0.54 MPa, lower than bio-columns produced from beach sand (1.85 MPa). The low porosity of the copper mine tailings limited the depth to which the MICP reaction could successfully occur, resulting in a 1.8 mm ± 0.4 mm crust forming around the outer extremities of the bio-columns. The results demonstrated that the particle size was a key deciding factor and that, as a result, MICP is not suitable for producing 'thick' bio-cemented materials from small particles (<100 µm) such as mine tailings. However, this method could produce thinner material such as bio-tiles or it could even be used to potentially cement together toxic dust particles typically formed on mine tailing heaps.

Manufacturing bio-bricks using microbial induced calcium carbonate precipitation and human urine.

In this study, we investigated the use of a natural process called microbial induced calcium carbonate precipitation (MICP) to 'grow' bio-bricks using the urea present in human urine. We first collected fresh urine and stabilized the urine with calcium hydroxide. This prevented any significant loss of urea which allowed it to then be used for the MICP process. We used Sporosarcina pasteurii bacteria to help drive the MICP process. The bacteria degraded the urea present in the urine to form carbonate ions which then combined with the calcium ions present in the urine solution to produce calcium carbonate. This calcium carbonate was then used as a bio-cement to glue loose sand particles together in the shape of a brick. The maximum compressive strength we obtained for a bio-brick was 2.7 MPa which compares well with conventionally made bricks. We successfully showed that human urine can be used to manufacture bio-bricks thus offering an additional use of human urine.

Treatment of textile wastewaters using Eutectic Freeze Crystallization.

A water treatment process needs to recover both water and other useful products if the process is to be viewed as being financially and environmentally sustainable. Eutectic Freeze Crystallization (EFC) is one such sustainable water treatment process that is able to produce both pure ice (water) and pure salt(s) by operating at a specific temperature. The use of EFC for the treatment of water is particularly useful in the textile industry because ice crystallization excludes all impurities from the recovered water, including dyes. Also, EFC can produce various salts with the intention of reusing these salts in the process. This study investigated the feasibility of EFC as a treatment method for textile industry wastewaters. The results showed that EFC can be used to convert 95% of the wastewater stream to pure ice (98% purity) and sodium sulfate.

Improved calcium sulfate recovery from a reverse osmosis retentate using eutectic freeze crystallization.

A novel low temperature crystallization process called eutectic freeze crystallization (EFC) can produce both salt(s) and ice from a reverse osmosis (RO) stream by operating at the eutectic temperature of a solution. The EFC reject stream, which is de-supersaturated with respect to the scaling component, can subsequently be recycled back to the RO process for increased water recovery. This paper looks at the feasibility of using EFC to remove calcium sulfate from an RO retentate stream and compares the results to recovery rates at 0 and 20 °C. The results showed that there was a greater yield of calcium sulfate obtained at 0 °C as compared with 20 °C. Operation under eutectic conditions, with only a 20% ice recovery, resulted in an even greater yield of calcium sulfate (48%) when compared with yields obtained at operating temperatures of 0 and 20 °C (15% at 0 °C and 13% at 20 °C). The theoretical calcium recoveries were found to be 75 and 70% at 0 and 20 °C respectively which was higher than the experimentally determined values. The EFC process has the added advantage of producing water along with a salt.