Anthropogenic activities are principally responsible for the manifestation of toxic and carcinogenic hexavalent chromium (Cr(VI)) triggering water pollution that threaten the environment and human health. The World Health Organisation (WHO) restricts Cr(VI) ions concentration to 0.1 and 0.05 mg/L in inland surface water and drinking water, respectively. The available technologies for Cr(VI) ions removal from water were highlighted with emphasis on adsorption technology. Furthermore, the characteristics of several polypyrrole-based adsorbents were scrutinized including amino containing compounds, biosorbents, graphene/graphene oxide, clay materials and many other additives with reported effective Cr(VI) ions uptake. This efficiency in Cr(VI) ions adsorption is attributed to enhanced redox properties, increased number of functional groups and well as synergistic behaviour of the materials making up the composite. The Langmuir isotherm best described the adsorption processes with maximum adsorption capacities ranging from 3.40–961.50 mg/g. The regeneration of Cr(VI) ions laden adsorbents was studied. Ion exchange, electrostatic attractions, complexation, chelation reactions with protonated sites and the reduction were the mechanisms of adsorption. Nevertheless, there are limited details on comprehensive adsorbent regeneration studies to prolong robustness in adsorption-desorption cycles and utilization of the Cr(VI) ions laden adsorbent in other areas of research to limit the threat of secondary pollution.

Sawdust is generated in large quantities in sawmills in Manicaland province in Zimbabwe, posing an environmental threat if incinerated or left to accumulate. This presents an opportunity for valorising the waste into briquettes. To make the briquettes cost effective, a cheap and locally available binder is needed. Hence, the use of banana waste pulp (green banana, ripe banana, pseudo-stem pith and fruit-bunch-stem) as a sawdust briquettes binder was investigated in this study. The quality of fabricated briquettes was evaluated based on relative density, shatter index, ignition time, burning rate, and time taken to boil a constant amount of water. The briquettes showed improved qualities with the increase in binder ratios. The sawdust-binder ratio of 1:4 showed the best briquettes qualities. Factor rating method was done in order to obtain the best scored (scale 0-100) briquettes reflecting weightier factors (scale 0-1). The weightiest factors were time taken to boil water (0.25) and shatter index (0.25), with three other factors weighing 0.5. The best five binder formulations in their order were; banana-pseudo stem-pith (pith) and ripe banana (RB) in the ratio of 3:1 respectively (score weight of 68.75), fruit-bunch-stem, banana-pseudo-stem-pith (pith), green banana (GB) and ripe banana (RB) in the ratio of 2:2:1:1 respectively (score weight of 68.3), banana-pseudo-stem-pith (pith), ripe banana (RB) and green banana (GB) 2:1:1 respectively (score weight of 66.95), banana-pseudo-stem-pith, ripe banana and green banana in the ratios of 2,5:1,5:1 respectively (score weight of 66.05) and banana-pseudo-stem-pith and ripe banana in the ratios of 1:1 (score weight 65.55).