# Filter Media-Packed Bed Reactor Fortification with Biochar to Enhance Wastewater Quality
## 3 Results and Discussion
### Monitored Wastewater Qualities
#### 3.2.1 Turbidity and pH  
It is known that grinding mineral-based matter can give rise to electrically unbalanced charges on their surface functional groups, for example, oxides (O\({}^{2-}\)) or hydroxides (OH\({}^{-}\)). As such, if such materials are immersed in solutions, they can bind some of the ions in the solution in order to become electrically balanced. This interaction has been found to be pH-dependent [37; 38]. Therefore, as an important indicator of chemical reactions, the pH was monitored for comparisons of the behaviors of the reference and fortified filters in interacting with the wastewater constituents. Figure 2 shows how the pH changed with time.  
As shown, fluctuations occurred in the pH of both the influent and effluents while a decreasing trend in pH of all effluents ensued from month 7. The mean influent pH (7.5) fell within an interval of pH 7.1-7.7. However, none of the lower bounds of intervals of all effluent pH measures fell within the influent pH range. This suggested that all the filters were still chemically active by the time the experiment was stopped. Further, the pH of effluents from all columns with GC was mostly \(>\)pH 8, a clear indication of the effect of high content of calcium in that material [39]. Some peaks occurred in influent pH whenever new wastewater was added to the ditribution tank thus showing that something in it spiked pH of the old water. This was probably due to the presence of alkaline substances such as detergents and dishwashing soaps. However, the pH in the storage tank tended to decrease slowly when it was kept longer. A most possible cause of this was the production of organic acids from the degradation of organic matter in the distribution tank [31]. Plots of turbidity as it changed with time are presented in log-scale in Figure 3.  
The Figure 3 shows that the influent turbidity was unsteady throughout the entire study. However, it seemed that the fluctuations did not affect the turbidity in the effluents. The inlet turbidity range was 29-907 NTU (Nephelometric Turbidity Units) while that for all effluents was 1-6 NTU. All the filters maintained \(>\)95% efficiency in reducing it, even when the inlet turbidity was extremely high. This means that concentrations of suspended solids and dissolved matter (organic matter and colored substances) were greatly reduced by the filters. Though the removal efficiency of Sa was slightly lower than those of other filters initially, it became better as the experiment was continued. The sieving effect of its pores probably improved as they were slowly cemented by the biofilm resulting from accumulating solids and organic matter [31]. Despite that, no signs of clogging were imminent by the  
Figure 2: Mean pH change with time for the entire study duration (In, inlet; Sa, sand; GC, gas concrete; C, biochar; SaC, sand + biochar; GCC, as concrete + biochar).  
end of the experiment. In general, the turbidity removal by all filters was acceptable according to WHO [40] guidelines on drinking water quality.