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Organic and/or heavy metal pollutants in soil and wastewater can be remediated by phytoremediation. Phytoremediation combines the disciplines of plant physiology, soil microbiology and soil chemistry. There are several ways by which plants extract, stabilize, filtrate, volatilize or degrade the contaminants. However, the effectiveness of phytoremediation relies upon the type of plant used. Pennisetum purpureum, commonly referred to as Napier grass, is one of the exceptional phytoremediators due to its rapid growth rate and ability to survive in highly contaminated soils. In the present review, the potential use and applicability of P. purpureum to remediate various contaminated areas was highlighted and comprehensively discussed, especially the five phytoremediation mechanisms involved (i.e., phytodegradation, phytoextraction, phytofiltration, phytostabilization, phytovolatilization). The application and management of P. purpureum in soil and wastewater phytoremediation were also critically presented. The coupling of phytoremediation and bioenergy is the zero-waste concept that can be applied since P. purpureum contains high lignocellulosic content that can be utilized as carbon source for biofuel production, such as ethanol and butanol.

The reason for such enormous efforts in palm oil mill effluent research would be what has been singled out as one of the major sources of pollution in Malaysia, and perhaps the most costly and complex waste to manage. Palm oil mill final discharge, which is the treated effluent, will usually be discharged to nearby land or river since it has been the least costly way to dispose of. Irrefutably, the quality level of the treated effluent does not always satisfy the surface water quality in conformity to physicochemical characteristics. To work on improving the treated effluent quality, a vertical surface-flow constructed wetland system was designed with Pennisetum purpureum (Napier grass) planted on the wetland floor. The system effectively reduced the level of chemical oxygen demand by 62.2 ± 14.3%, total suspended solid by 88.1 ± 13.3%, ammonia by 62.3 ± 24.8%, colour by 66.6 ± 13.19%, and tannin and lignin by 57.5 ± 22.3%. Heat map depicted bacterial diversity and relative abundance in life stages from the wetland soil, whereby bacterial community associated with the pollutant removal was found to be from the families Anaerolineaceae and Nitrosomonadaceae, and phyla Cyanobacteria and Acidobacteria.

Phytoremediation is one of the environmental-friendly and cost-effective systems for the treatment of wastewater, including industrial wastewater such as palm oil mill effluent final discharge (POME FD). However, the effects of the wastewater on the phytoremediator plants, in term of growth performance, lignocellulosic composition, and the presence of nutrients and heavy metals in the plants are not yet well studied. In the present work, we demonstrated that POME FD increased the growth of P. purpureum. The height increment of P. purpureum supplied with POME FD (treatment) was 61.72% as compared to those supplied with rain water (control) which was 14.42%. For lignocellulosic composition, the cellulose percentages were 38.77 ± 0.29% (treatment) and 34.16 ± 1.01% (control), and the difference was significant. These results indicated that POME FD could be a source of plant nutrients, which P. purpureum can absorb for growth. It was also found that the heavy metals (Al, As, Cd, Co, Cr, Ni and Pb) inside the plant were below the standard limit of the World Health Organization (WHO). Since POME FD was shown to have no adverse effects on P. purpureum, further research regarding the potential application of P. purpureum following phytoremediation of POME FD such as biofuel production is warranted to evaluate its potential use to fit into the waste-to-wealth agenda.

Average of about 53 million m3 POME is being produced yearly in Malaysia. The treated palm oil mill effluent (POME) will be discharged to the river. However, the POME final discharge still contains high oxygen demand (COD) and suspended solids (SS) that potentially to cause environmental issues. Therefore, the aim of this study is to treat the POME final discharge with Napier grass (Pennisetum purpureum) in the constructed wetland system. This study has been carried out to investigate the feasibility of the Constructed Wetland in polishing the final discharge according to river quality index. Besides, the propagation of Napier grass in the POME final discharge was evaluated. Four different physicochemical parameters such as chemical oxygen demand (COD), total suspended solid (TSS), ammonia and colour were analysed based on standard laboratory methods and procedures. Results revealed that the reduction of COD level by 71.57 %, TSS by 83.59 %, ammonia by 85.97 % and colour reduced by 87.62 % after 15 days treatment time. In term of propagation of plant, Napier grass showed an excellent propagation in POME final discharge by 13.94% increment. The overall results indicated that treatment of POME final discharge by using Napier grass constructed wetland was successful to reduce the concentration of the contaminants.