# Brown Coconut Husks as Media Within an Anaerobic Filter for Improving On-Site Wastewater Treatment
## 4 Discussion  
When proposing a new appropriate wastewater treatment process, it is important to evaluate the solution based on several aspects. The ability to provide treatment and improve wastewater quality is key, and this is evaluated by measuring the COD removal. Ensuring that there are no adverse effects to the environment is also crucial, so the leaching of nutrients has been tested. Finally, the practical feasibility needs to be considered because if the maintenance requirements are not feasible, then the solution will not improve the situation and may cause more problems. While this study was not conducted for a period long enough to establish the frequency of maintenance, it does provide an indication, and suggestions for future research directions are given later in this section. Typical COD removal by anaerobic filters containing coconut husks or coconut shells range from 49% to 73% [16; 17; 18; 20; 26], as summarized in Table 2. The exception is [PERSON] et al. [20], where fresh green coconut husks were tested, and due to the leaching of COD from the coconut husks, the resulting removal was only 21%. The dried green coconut husks evaluated by [PERSON] et al. [16] appear to behave in a similar way to the brown coconut husks (Table 2). The COD removal for this study (Figures 2 and 3) is similar to others reported in the literature (Table 2). Typically, studies reporting on reactor performance report the overall average, so it is not possible to know whether an improvement in treatment performance over time was observed as seen in this study. By examining the performance over time, it has been revealed that it takes several months for the biofilm to form, with the maximum performance measured after 9 months (Figure 3); however, longer-term trials are required to determine whether performance continues to improve. Figure 7: Photographs of the coconut husk at the end of the 10-month reactor trial showing the inside of the reactor once the water had been drained (**A**), the biofilm on a piece of coconut husk (**B**), and a coconut fiber examined under a microscope (**C**). An anaerobic filters serve as a secondary treatment step in household wastewater disposal systems. Their primary function is the removal of COD from wastewater rather than the elimination of nutrients. Consequently, it is anticipated that there will be no observable change in nutrient levels in the effluent following treatment with the anaerobic filter. However, because the brown coconut husks are organic material, it is important to test whether nutrients are leached, which may have a negative impact on the environment. According to the Australian Guideline for Sewerage Systems [27], typical nutrient levels in secondary treatment effluents range from 20 to 50 mg TN/L and 6 to 14 mg TP/L for nitrogen and phosphorus, respectively. Both nitrogen and phosphorus levels in the effluent of this study fall comfortably within this specified range. It is important that these nutrient levels are below the threshold to prevent eutrophication. Often, effluent from septic tanks enters the environment via a leach field, and therefore, the impact to the environment is site-specific, depending on the soil type and the presence of groundwater, and additional treatment systems would be needed if nutrients were a concern. The presence of any sensitive ecosystems such as coral reefs should also be considered [4]. Conversely, if the effluent was used as irrigation water for crops, then the presence of nutrients may be an advantage. It is important to note, however, that cultural considerations need to be carefully investigated with the community before the reuse of treated wastewater occurs. One key consideration in terms of the feasibility of this solution is the longevity of the filter media. The coconut husks used in this work had not started breaking down after 10 months. It has been suggested in the literature that coconut husks can be used in anaerobic filters for at least 2 years [18].