Potential use of pumice rocks for municipal and industrial wastewater treatment in Tanzania

Globally, there are several municipal wastewater treatment technologies that have evidently proved a success. In Tanzania, for instance, the waste stabilization pond is the leading municipal wastewater treatment technology, while industries have different wastewater treatment setups. However, the effluents from most WSPs have been reported to not comply with the statutory discharge limits. This has prompted efforts from scientific and industrial communities to focus on seeking alternative technologies to address this challenge. This research was carried out to assess the potential of pumice rocks as treatment media for textile and municipal wastewater`s biological oxygen demand (BOD) and chemical oxygen demand COD. The study aimed at examining the capacity of pumice rocks in reducing the BOD5 and COD of both municipal and textile wastewater, and colour reduction from textile wastewater. Both effluents were treated in a lab-scale, 4560 cm(3) column packed with 800 gm cream, lightweight, porous and high silica content (55.7% (w/w) SiO2) pumice rocks. Based on the column capacity, the 3500 cm(3) of effluent was discharged into the column under gravitational force at hydraulic retention time of 24, 48 and 72 h at room temperature. BOD5 and COD were analyzed by the respiratory and closed reflux methods, respectively, while colour reduction from textile wastewater was monitored by UV-vis. Pumice rocks were characterized by FTIR, XRF and XRD. The results showed that pumice is composed of a high content of silica (silicon dioxide) of about 55.7% with some alumina (aluminium oxide) and traces of other oxides. XRD results suggest that pumice is mainly composed of amorphous silica with some crystals of natural zeolite. These results were well complemented with FTIR results. Pumice materials reduced the BOD5 and COD of municipal wastewater initial values by 65.2% and 76.2%, respectively, after 72 h retention time. On the other hand, pumice rocks seemed to be more effective in reducing the BOD5 and COD of textile wastewater. The results show that BOD5 and COD of textile wastewater were reduced by 75.7% and 93.5%, respectively, after 72 h retention time. Moreover, pumice rocks could reduce the colour/turbidity of textile wastewater by 81.8% after 72 h retention time. These results are promising and displayed the potential of pumice, a naturally occurring material, in wastewater treatment. It is envisaged that pumice materials could be integrated into the municipal or industrial wastewater treatment facilities. It is recommended that studies on a continuous flow reactor are conducted to investigate the effect of flow dynamics and adsorption kinetics on the treatment of wastewater by these materials.