ENGINE OIL

The hardening of low carbon steel through heat treatment has a rich historical context and is an essential aspect of metallurgy that has been practiced for centuries. The process of hardening steel involves heating it to a specific temperature, known as the critical temperature, and then rapidly cooling it, often through quenching in water, oil, or other mediums. This process alters the internal structure of the steel, enhancing its
hardness and strength. Traditional quenching mediums include water, but the growing interest in exploring alternative options like vegetable-based oils (engine oil) and MN brine solution due to environment and sustainability consideration.

This study was carried out to assess the effect of spent engine oil on the growth of two microalgae Monoraphidium contortum and Dimorphococcus lunatus. The test algae were grown in seven concentrations of 0% (control), 5%, 10%, 25%, 50%, 75% and 100% which were set up in triplicates. The growth response was monitored every two days for 14days using a visible spectrophotometer (Model No. HV-721). The percentage inhibition, percentage yield, growth rate, and cumulative growth rate and analysis of variance (ANOVA) were calculated using Microsoft Excel software. Physicochemical parameters were also assessed including, pH, total dissolved solids and electrical conductivity using prescribed methods. The results obtained showed that both microalgae species exhibited a positive growth response to the WSF, with Monoraphidium contortum consistently demonstrating higher growth compared to Dimorphococcus lunatus across all tested WSF concentrations. Statistical analysis using ANOVA indicated no significant difference (p > 0.05) in growth response among the various WSF concentrations for both species. However, temporal differences between measurements were statistically significant (p < 0.001). Percentage inhibition analysis revealed growth stimulation at low concentrations (5%, 10%, 25%, and 50%) and inhibition at high concentrations (75% and 100%) for both species, with Monoraphidium contortum showing higher inhibitory response relative to Dimorphococcus lunatus. Algal yield was enhanced at low to high concentrations (0-75%) for Monoraphidium contortum and low to moderate concentrations (0-50%) for Dimorphococcus lunatus. Growth rate analysis consistently favored Monoraphidium contortum across all WSF concentrations tested. Cumulative growth rate analysis suggested that Dimorphococcus lunatus may be less tolerant to WSF components compared to Monoraphidium contortum. Furthermore, total dissolved solids, electrical conductivity, and pH increased significantly on termination of the experiment. Based on the findings of this study, both microalgae showed bioremediation potentials and should be further studied