Low-Tech Coconut Shell Activated Carbon Filter

By Ami Cobb and Mikell Warms -- We discovered our passion for water resource management, specifically water quality in the developing world, during our college career at Santa Clara University. As undergraduate engineering students, we were required to submit a senior design project highlighting our interests and the knowledge we gained during our four years of study. blueEnergy was introduced to us during this period, and as part of the senior design process, we had the incredible chance to visit Bluefields, Nicaragua in order to fulfill our project goals. Our project was a low-tech coconut shell activated carbon filter. Simply put, it’s like a Brita filter that can reduce pesticides, tastes, and odors in drinking water.

Mikell attacking the charcoal dilemma

Activated carbon in the United States is often produced using steam activation, a process that requires temperatures ranging from 900-1200˚C. It produces a high quality activated carbon, yet cannot be produced in places such as Bluefields or other remote developing locations. Through our research we found that chemical activation could be used to produce activated carbon at lowered temperatures of 300-500˚C. We also learned that coconut shells were the best carbon media that one could use to produce activated carbon, and since they are so abundant in Nicaragua, we were in luck! While in Bluefields, we burned coconut shells using the oil drum method, which is currently used to produce charcoal for cooking purposes, and then attempted to chemically activate them using calcium chloride, an inexpensive and readily available chemical in the United States. After a week and a half in Bluefields, we were finally successful using this technique. We knew that our carbon had in fact been properly activated by using methyl orange, a soluble organic chemical indicator. A reduction in the orange tint of a methyl orange solution, after it has been treated with the activated carbon, is a very positive indication that it will also reduce pesticides and other organics in the water. Since pesticides are insoluble, they have a greater affinity for activated carbon than a soluble organic chemical, such as methyl orange. Thus if our activated carbon could adsorb the methyl orange, it could adsorb pesticides at an even higher rate.

However, it was a bittersweet accomplishment since we understood that calcium chloride would probably not be found at the local market. In a desperate attempt to salvage the situation (and ingenious if we do say so ourselves), we tried sodium chloride (table salt) knowing that calcium chloride was also a salt. It’s cheap, readily available, and as we found out, another agent which can activate carbon! Once we returned to the labs at Santa Clara University, we did quantitative experimentations using a spectrophotometer and, as expected, found that it was not as good as the high quality carbon that is manufactured in the United States, but it was indeed successful and yielded comparable results to the charcoal activated with calcium chloride.

Ami filling the barrel with coconut shells

Although Bluefields was our pilot location, we hope that our activated carbon can eventually be applied in developing countries globally. At blueEnergy, we will probably be remembered best as the only volunteers to ever wash Cookie (a very old, slightly senile blueEnergy guard dog), but we hope our project will inspire people to filter their water in a simple and inexpensive fashion. Apart from making progress on our project in Bluefields, we had an unforgettable experience with the exciting culture and the new people, and we would like to thank all the employees and volunteers for helping out in any way and cheering us on. 

Thanks Ami and Mikell!