Investigation about arsenic in Costa Rica

In the months September until November, we (Roald van der Ven & Marten Bosma) received the opportunity to do our self-composed minor program abroad. As a civil engineer, Central America is very interesting regarding drinking water. Therefore, we did a research project at the TEC (Tecnológico de Costa Rica) in Costa Rica. This minor contained an investigation about arsenic which is present in the potable water of Costa Rica. Arsenic present in the water can lead to serious health risks such as cancer on long term exposure.

The World Health Organization (WHO) has recommended an arsenic level which has a lower concentration than 10 μg As/L for safe drinking water. Most of the drinking water in Costa Rica has a value of arsenic present in the water that exceeds this maximum value. Presence of arsenic is caused by volcanic eruption, which increases the amount of arsenic in the groundwater.

During our investigation, we focused on the treatment set up of the groundwater at La Rueda Condominio. The current operating system was functioning by a chemical process using GreensandPlus. Previous research done by Niels Walrave presented a recommendation of improving the backwash frequency. Analysis of the improved system showed us an arsenic concentration lower than the recommended 10 μg As/L.
While analyzing the chemical system, we also focused on designing a new treatment set up. This set up contains a biological process for the treatment of groundwater. The designed set up makes use of bacterial growth for the oxidation of As(III) to As(V). For the occurrence of this process, pumice is used, which is a volcanic stone that contains a high porosity. After running the system for a short period of time of around two weeks, oxidizing bacteria will grow on the pumice.

The complete set up contains an aeration tank, two vessels and a ferric chloride dosingpump. The water flows into the aeration tank for a higher oxygen concentration and flows then into the pumice vessel. Subsequently the water receives a small ferric chloride dosage before passing through the second vessel which is filled with sand for filtration.
Because we spend a lot of time on reading papers about different types of treatment setups, we did not had much time to run the biological system at the end. Therefore we tested the system in its starting phase where small amounts of oxidation from As(III) to As(V) takes place. However, in order to get useful results a longer runtime of the biological pilot system is necessary.

Roald van der Ven & Marten Bosma