Optimization of hydraulic efficiency and wastewater treatment performances using a new design of vertical flow Multi-Soil-Layering (MSL) technology

The study gives a new method for contaminants removal from domestic wastewater using a novel design of Multi-Soil-Layering (MSL) eco-technology. Two MSL reactors were built and operated under laboratory conditions: a standard and modified MSL design (S-MSL and M-MSL). A tracer test using KCl indicated varying degrees of dispersion, short-circuiting, dead space, effective volume ratio and hydraulic efficiency in two MSL reactors. The new MSL design was found to be most effective in improving hydrodynamic flow conditions. The M-MSL reactor increased the mean HRT from 15.79 to 22.07 h, and decreased the dead space rate from 38% to 8%. The early arrival of the distribution peak, indicator of short-circuiting, was mainly noted in the case of S-MSL RTD which is around 57% of the nominal HRT. A high dead space rate was found to occur in the S-MSL reactor, and produced a poor hydraulic performance. The large difference between the nominal and mean HRT confirms the presence of zones of stagnation in the S-MSL system. The new MSL design increased the effective volume ratio from 0.62 to 0.92. The hydraulic efficiency was increased from 0.26 to 0.84 and reached a good level (λ ≥ 0.75) highlighting the excellent hydraulic performance of the M-MSL design. Obtained results revealed that M-MSL had an optimal hydraulic profile and enhanced sanitary and physicochemical performances compared to S-MSL. The mean log reduction of total coliforms, fecal coliforms and fecal streptococci was increased from 1.25, 1.26 and 1.15 log units for the S-MSL to 2.36, 2.38 and 2.11 log units for the M-MSL reactor. Both MSL reactors achieved high and satisfactory TSS and organics removal. The M-MSL reactor accomplished a 92% removal of TN, while the S-MSL achieved a slightly less effective result. The M-MSL reactor was also found to be more efficient in reducing TP by 98% compared to a removal rate of 76% in the S-MSL reactor. Therefore, the new design of MSL eco-technology could be adopted as an alternative to the current design for efficient domestic wastewater treatment.