# Brown Coconut Husks as Media Within an Anaerobic Filter for Improving On-Site Wastewater Treatment
## 3 Results and Discussion
### Nutrient Levels in the Effluent  
The nutrient concentrations in the effluent are influenced by several processes including uptake by the biofilm, biological and chemical processes, which change the form of compounds containing nutrients, and the potential leaching of nutrients from the coconut husks within the filter. Previous research showing COD release from coconut husks [20] suggests that the leaching of nutrients should be investigated. To reveal changes in nutrient concentrations, the synthetic wastewater feed and the effluent were compared (Figure 4). An increase in the nutrient level in the effluent relative to the feed suggests potential leaching. The forms of nitrogen included total nitrogen, ammonium, and nitrate; however, during the measurements, there was no nitrate detected, so only the total nitrogen and ammonium are shown in Figure 4 along with total phosphorus. Note that the changes in nutrient concentrations in the feed within the first 25 days are due to the start-up procedure. The data collected for total nitrogen show variation particularly towards the start of the experiment (Figure 4A). Some of this variation might be due to the washout of cow manure from the inoculation process. It is also possible that any particulate material from the coconut husk pieces was flushed out at the start of the process, which would have been detected in the analysis of total phosphorus and total nitrogen. The ammonium concentration was consistently higher in the effluent of the reactor compared to the feed  
Figure 4: Comparison of total nitrogen (**A**), ammonium (**B**), and total phosphorus (**C**) concentrations in the synthetic wastewater feed (blue) and effluent (green). (Figure 4B). It is possible that the increase in ammonium is due to the transformation of nitrogen present in the synthetic wastewater into ammonium. The two key nitrogen-containing components in the synthetic wastewater are milk protein in the dried milk and urea [21]. Milk proteins can be broken down into ammino acids, and then, ammonium and urea can hydrolyze into NH\({}_{4}\). However, to confirm this, additional experiments are needed to confirm that leaching from the coconut husks is not occurring. Figure 4C shows a variable result in total phosphorus levels in the effluent compared to the feed at the beginning of continuous reactor operation and then fairly consistent levels from day 25 onwards. This is likely due to the initial washout of the cow manure, but some leching may also be occurring initially. Once the reactor stabilized, there was very little difference between the feed and effluent concentration (Figure 4C), indicating no significant leaching occurring long-term. Nutrient Leaching from the Coconut Husk  
The presence of nitrogen and phosphorus within the synthetic wastewater may have been masking some leaching from the coconut husk. To eliminate the synthetic wastewater contributing to the nutrient levels, an additional experiment was conducted where RO water was used as the feed using a reactor, which was set up and run in the same way as the first continuous anaerobic filter. This would then determine any leaching of nutrients from the coconut husks. The nutrient levels in the effluent of this reactor are shown in Figure 5.  
Some nitrogen and phosphorus initially leached from the coconut husks, but this was quickly washed out of the reactor (Figure 5). Very little ammonium was detected (Figure 5A), which indicates that the nitrogen being leached is in another form. This finding also suggests that the increase in ammonium shown in Figure 4B was due to nitrogen sources within the synthetic wastewater feed being broken down within the anaerobic filter. Some phosphorus was initially leached (Figure 5B), but this reduced quickly to a low ongoing amount of phosphorus leaching. This ongoing level of leaching is insignificant compared to the level of phosphorus typically found in domestic wastewater and was not apparent in the reactor, which was fed with synthetic wastewater (Figure 4C).