Phytoremediation of Copper as a Micro Nutrient
(University of Minnesota – Duluth)
As the use of copper as a replacement for aluminum for circuit interconnects on high performance microprocessors through barrier seed copper deposition, electroplating and dielectric deposition, and chemical mechanical planarization (CMP) become more mainstream for the semiconductor industry, removal of the copper ion from large volumes of CMP wastewater has become a crucial issue. The semiconductor industry, which produces copper laden wastewater, is forced to cope with copper-toxicity issues and stringent regulations on copper effluents.
The traditional way for industrial wastewater treatment facilities and publicly owned treatment works to deal with copper discharge in wastewater is through advanced filtration methods. These include reverse osmosis, electro winning techniques, and ultra filtration or hollow fiber absorption, which have high operational and capital costs.
Through biological processes, some plants are capable of selectively removing copper from a contaminated medium and assimilating it into its tissue. Current research and application in phytoremediation has received a lot of attention and is showing promise for remediation of soils and waters contaminated with toxic metals.
This research is to explore the feasibility of a biosolid, land application process and operation as it applies to remediation of high copper concentration chemical mechanical planarization (CMP) wastewater, through investigating the phytogenic conversion process which transforms copper from an expensive to remove, heavily regulated pollutant into a commercially viable and valuable micronutrient.
Cotton has been selected as the test crop for this research. A preliminary study has demonstrated that cotton plants can survive high dose copper exposure administered in a laboratory environment. The proposed research will expand on these findings and determine if cropland application is a feasible alternative for Cu-containing wastewater. The commercial production of cotton requires large amounts of water and nutrients, and many large generators of copper-containing wastewater are located in cotton growing regions.
The test will begin upon cotton seedling transplantation into the test soil mixture. The experiment matrix will consist of 4 sets of 12 plants. Control group #I will be cultivated with just soil and DI (de-ionized) water, and control group #2 with a soil-biosolid mixture and DI water. Experimental group # 1 will be grown in a soil medium with chemical mechanical planarization (CMP) slurry, and experimental group #2 in a soil-biosolid medium with CMP slurry. The CMP slurry used will be from an actual planarization process waste-stream from integrated circuit manufacturing done in California. Plants will be given a daily copper dose based on slurry concentration and annual precipitation/irrigation requirements for cotton grown in Califomia’s San Joaquin Valley. Parameters to be measured include plant height, number of leaves, boll fommation, and health.
The cotton plants will not reach maturity in time for a quantitative analysis to be conducted on the soil, plant tissues, and cotton fibers to determine the end locations and concentrations of copper in time for the paper deadline. However, there will be enough plant data available that preliminary conclusions can be drawn. Reported results will be based on the available plant growth, leaf, and fruit development data.
The research however will continue on and take the plants full term, where a more detailed analysis can take place. Once the cotton crop reaches maturity, the plants will be harvested and a mass balance for copper will be conducted using flame atomic absorption spectroscopy. A comparison analysis will be done upon completion, and based on the findings, conclusions will be drawn as to the success or failure of copper remediation by cotton.
This process introduces copper as a valuable soil amendment used by plants in the formation of plant tissue. It will also redefine copper as a nutritional constituent in a biosolid product, leaving an opportunity for copper rich biosolids to improve crop yields and plant health where native soils are low in copper and are heavily irrigated. This application of copper rich biosolids to commercial cotton crops will hopefully result in permanent destruction of waste with lower costs than other types of treatment.