Civil Engineering Project Topics

Effects of Addition of Carbide on Sewage Degradation

Effects of Addition of Carbide on Sewage Degradation

Effects of Addition of Carbide on Sewage Degradation

Chapter One

Objective of Study

The objective of this project is to investigate the effect of addition of carbide on sewage degradation.



Effects of Chemicals on Sewage Treatment

Riad et. al. (2012) studied the potential use of carbide lime waste (CLW) for wastewater treatment. The main characteristics of the CLW were determined. Chemical and X-ray diffraction analyses indicated that CLW was similar in chemical and mineralogical compositions to industrial lime, except for the presence of carbon in the waste. Morphological and elemental chemical analyses by scanning electron microscopy and energy dispersive X-ray spectrometry also revealed that CLW particles differ from industrial lime by the presence of carbon formations. The use of CLW was evaluated in the treatment of Annaba city wastewater effluent. CLW was found to be the most suitable for the treatment of Annaba city wastewater for an optimal dose of 850mgL. Percentage removal efficiency for turbidity, total suspended solids (TSS), chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD5) was found to be 96, 98.2, 90 and 84.5%, respectively. Residual turbidity in supernatant was 4.5 NTU and total residual bacteria was 68CFUmL. Algerian effluent quality standards for TSS and COD were met after treatment. However, BOD5, bacterial level and pH were high, emphasizing the need for pH adjustment and secondary treatment for the Annaba city effluent. The precipitation of heavy metals with CLW was shown to be successful in reducing the level of soluble heavy metals in aqueous solution. The removal of heavy metals was enhanced at pH ranges 10-11 for zinc, 9.2-11.6 for lead, 4-11.8 for iron and 7-11.8 for copper. The results revealed that CLW could be effectively used in wastewater treatment.

Ip and Jowett (2004), carried out a field experiment to quantify the effects of household chemicals. This was carried out using low strength wastewater dosed at a diurnal rate to four 100 L pilot-scale septic tanks and calibrated to four-day residence time. Mixtures of detergent with bleach and bleach pucks were used, with dose concentrations calibrated to tank size and to laundry or toilet volumes. After a one-week start-up period, chemicals were dosed for 2 weeks, stopped for 2 weeks (by accident), and started again for 4 weeks, followed by 2 weeks of no chemicals. The experimental run was divided into two sets, Set A with no chemicals dosed and Set B with chemicals dosed. Average %BOD removals were calculated at each sampling day and a “paired t-test” was employed to compare the significance of the differences between Tests and the Control for each set. The paired t-test on BOD removal rates showed that for Set A (no chemicals dosed) there were significant differences between the pilot-scale septic tanks receiving detergent (ST-1 – 75% poorer removal efficiency) and BOTH chemicals (ST-4 – 71% poorer removal efficiency) at the 95% confidence level, primarily due to the divergent effluent BOD concentrations found at the beginning of the experimental run. Towards the end of the experimental run, after chemical dosing was ceased, all pilot-scale septic tanks seemed to perform equally indicating that septic tanks recover quite readily. ST-3 receiving flush puck solution (29% poorer removal efficiency) showed no significant difference compared to the control. The paired t-test for Set B showed that the differences between ST-1 (88% poorer removal efficiency) and ST-4 (200% poorer removal efficiency) compared to the Control were significant at the 95% confidence level. The addition of flush puck solution (ST-3) seemed to actually improve %BOD removal (31% higher removal efficiency), but the difference was not statistically significant compared to the Control. Fecal coliforms were typically lower than the Control, but not diagnostic, suggesting no widespread ‘kills’ at these levels of chemical addition. Dead septic tanks were caused by greater use of disinfectants than used in this experiment.

Gross (1987), determined the amounts of specific household chemicals required to completely destroy bacteria in a septic tank.  The household chemicals used in this study included: liquid chlorine bleach, HTH (high test hypochlorite), Lysol and Drano Crystal.  Domestic septic tanks were dosed with different concentrations of chemicals to determine the amount required to completely destroy the entire microbial population.  The effectiveness of each chemical was assessed by measuring the decrease in total coliform units with respect to concentration of disinfectant and time.   Gross found that slug dosages of chemicals are more harmful than gradual dosages and that the microbial populations recovered quickly after the disinfectant doses were stopped.

The work of Washington et al. (1998) had the primary objective of determining the fate of absorbable organic halide from household bleach in a septic system and a secondary objective of assessing the effect of bleached laundering on septic tank performance.  The COD removal efficiency was used as the measure of septic tank performance.  Total coliforms concentrations were used as the measure of septic tank health.  It was found that the COD removal was 40-50% in the septic tank prior to laundry addition whereas COD removal of only 25-35% was attained after the addition of laundry wastewater (bleached and unbleached).  However, they found no statistical difference between total coliforms in the septic tank receiving bleached or unbleached laundry.






Collection of Samples and Description of Experimental Set Up

Sewage sample was collected from the University of Nigeria, Nsukka waste stabilization pond for laboratory analysis. Six experimental set ups labelled A, B, C, D, E and F were constructed in the sanitary laboratory. Each set up contained five litres of sewage. The A set up served as control without calcium carbide while B,C,D,E, and F set ups contained 1g, 2g, 5g, 8g and 10g of fresh calcium carbide respectively.

Samples were collected from each of the six different set up twice per week for two months for laboratory analysis to determine the concentrations of BOD, COD, suspended solids, pH and total coli form. Date of collection was recorded for all the samples collected.



The results from the laboratory are presented in Figures 4.1-4.5 and Tables A1-A5 while the statistical results analysis is shown in Tables 4.1-4.7. The results are analysed below:




  1. Addition of calcium carbide caused a gradual reduction of BOD and COD in the sewage.
  2. Addition of carbide reduced the number of positive test bacteria while there was a gradual increase in pH value.


A further treatment should be carried out as this experiment could not establish a 100% treatment of sewage.


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