Coffee grounds as an adsorbent for heavy metals in water treatment : Study based on the environment around Vattenriket, Kristianstad

Abstract: One of the modern times worst environmental problem are polluted water resources. An example of source of pollution to water resources are, heavy metal leached from acid sulfate soils (ASS). When these soils are stable, which they are if they are left underwater in an anoxic environment (for example below the water table), they are often sought after since they consist of high amount of nutrients which farmers use as farmlands. ASS is therefore created when farmers drain their land and the sulfide soil gets exposed to air, resulting in its oxidation and therefore formation of sulfuric acid. In a previous study performed by scientists from Linnaeus University, it was concluded that a natural reserve located in Vattenriket, Kristianstad was possibly damaged by the drainage discharge of an adjacent acid sulfate soil. For remediation of acid sulfate soil, notably removal of metals from drainage waters, grounded coffee has been suggested to be able to perform well as an adsorbent. This study was performed to investigate how well grounded coffee could be used as an adsorbent, for calcium (Ca) and zinc (Zn), from water samples collected in Vattenriket, Kristianstad. It was also studied to see if grounded coffee could be cleaned using a sodium hydroxide solution to increase its adsorption capacity. To be able to evaluate how well it could be used as an adsorbent, it went through two different cleaning procedures and total organic carbon and pH readings was performed. The used method for this paper was to clean the grounded coffee in two different stages. The first stage consisted of using distilled water and letting it run through the residues until the water came out as transparent. Cleaning using a NaOH solution consisted of suspending the residues in a NaOH solution for 45 minutes and swapping the solution 6-8 times. After the grounded coffee had dried in an oven at 30o for 48 hours, it was put into different fraction sizes, weighed and bagged. The water samples then had to be filtered using a pump and Filtropur S 0.45 filters. Lastly, 45 falcon tubes containing 15 different amounts of grounded coffee had 50 ml of filtered water sample added to them. For analysis, atomic absorption spectroscopy was used. The results showed that the maximum amount of adsorbed calcium was achieved at 1.5g of grounded coffee in a 50 ml water solution which managed to adsorb 99.53% of calcium. The maximum amount of adsorbed zinc was achieved at 1.25g of grounded coffee in a 50 ml solution which resulted in 99.16% of adsorbed zinc. The study also showed that when the total organic carbon-content was decreasing, due to excessive cleaning, the pH was increasing. This was further proof that the grounded coffee still had residues onto its surface that could inhibit its adsorption capabilities.