Department: Agricultural And Bio-resources Engineering
Okoye, N. M.
Nwuba, E. I. U.
Madubuike, C. N.
Substrates play an important role a Constructed wetland (CW). There has been a growing interest in the use of non-conventional materials as CW substrates. Palm kernel shell have been reported to have the capacity to serve as a wetland substrate. Its use in CWs will lead to a beneficial reuse of the by-product. Therefore, the aim of the study is to explore the potential of a palm kernel shell based field-scale horizontal subsurface flow CW for on-site bio-remediation of slaughterhouse effluent. To this end, several research tools including pilot and field-scale studies and computational fluid dynamics modeling were employed. Preliminary studies were conducted with a view to ascertaining the growth and treatment performance of three macrophytes, and the suitability of palm kernel shell as a CW substrate. Six pilot horizontal subsurface flow CW cells were built and planted with three macrophytes Typha latifolia, Thalia geniculata and Colocasia esculenta. Four of the cells were filled with gravel, while two were filled with palm kernel shell. Influent and effluent wastewater samples were collected and evaluated for key physicochemical parameters. To estimate k-C* design model constants, three horizontal subsurface flow CW columns were built and the model constants obtained by fitting the model predictions to the measured concentrations in the column. A palm kernel shell based field-scale horizontal subsurface flow CW was constructed and monitored for key physicochemical parameters. The hydrodynamic behaviour of the field-scale CW was evaluated using tracer test. Also two Dimensional (2D) computational fluid dynamic modeling using finite element-based commercial software COMSOL Multiphysics 5.3a was employed to further evaluate the hydrodynamic behaviour of the system, and to simulate the influence of different hypothetical configurations to optimize residence time. The preliminary study revealed that Thalia Geniculata was the most suitable macrophyte specie for CW with palm kernel shell. It also revealed that palm kernel shell had a treatment efficiencies of 72.81% for BOD; 89.87% for TSS; 39.42% for NH4-N; 60.79% for NO3-N and 42.52% for PO43- comparable to values of 75.42% for BOD; 88.18% for TSS; 41.33% for NH4-N; 55.86% for NO3-N and 44.73% for PO43- obtained for gravel. The palm kernel shell based field-scale horizontal subsurface flow CW significantly reduced pollutant concentration of the slaughterhouse effluent, with average removal rates of 81.07% for BOD, 82.12% for TSS, 46.03% for NH4-N, 38.13% for NO3-N and 40.92% for PO43-. The hydrodynamic evaluation showed that water fluxes were not homogeneous, but that the system had a good hydraulic efficiency. The computational fluid dynamic modeled tracer response curve showed good agreement with the experimental results, with a correlation coefficient of 0.99. It also revealed that vegetation layout within the wetland was the most effective modification for improving the hydrodynamics, thus should be given adequate consideration during the design phase. The study concluded that palm kernel shell based field-scale horizontal subsurface flow CW improves effluent quality, with removal rates comparable to that of conventional wastewater treatment systems, thus should be used protect sensitive water bodies that receive slaughterhouse effluent. It has provided rigorous field data and information to support its implementation. The study recommends long term (5 to 10 years) performance evaluation of palm kernel shell substrate, with a view to determining the magnitude of its lifespan.