Sustainable treatment of waste using recycled chitosans
The Sustainable Treatment Of Waste Using Recycled Chitosans (STOWURC) project is developing sustainable materials and processes that use waste products from the seafood industry to treat waste streams and recover metals from the printed circuit board (PCB) and related industries.
The UK PCB industry is strategically important to the country but its chemical processes can generate waste products that are expensive to treat. The shells of crabs and other crustaceans are a source of materials known as chitosans which can absorb metals and have the ability to recover metals found in PCB manufacturing effluent. The UK’s seafood industry generates large volumes of shellfish waste and the project is using this waste to produce chitosan-based materials that can sustainably treat the effluent produced by PCB makers and companies producing similar types of metal-bearing waste products.
The project partners have identified international interest in using chitosan based materials from PCB manufacturers. There are also much larger applications in other sectors, including surface engineering. Crab shells are typically expensive to dispose of and this project will enable them to become valuable raw materials.
C-Tech has been involved with all aspects of the R&D activity in the STOWURC project. This has entailed everything from milling and sizing of stabilised crab shells received from Kynance Cornish Crab, our partner in the seafood industry, to evaluating chemical routes for the production of crab shell derivatives, and testing and modelling the performance of these and other materials in the target application of treating copper bearing waste water streams arising in the printed circuit board and metal finishing industries.
Working at increasing scale (rising to c.a. 50kg lots) over the course of the project we have prepared multiple lots of ground crab shell for treatment and testing by mechanical milling, and have optimised the particle size range for both product yield and performance. In the case of a packed bed filtration bed type process, a relatively large particle size (~0.85–3.5 mm) is actually preferable to finer fractions. Working with our project partners at A-Gas Electronic Materials, we have systematically looked at a range of candidate approaches to the stepwise demineralization (removal of calcium carbonate) and deacetylation (conversion of chitin to chitosan) of crab shell, and evaluated the relative performance of a range of samples at intermediate and final stages of this treatment cycle. The findings of this work have been built into the project’s cost/benefit calculations for a range of crab shell derived materials.
On the basis of initial laboratory trials, C-Tech was able to define outline process requirements for a continuous mode effluent treatment unit operation, and then specify and procure a suitable small scale first pilot unit for laboratory and in-the-field (factory) testing with our PCB industry end user partner Amphenol (Invotec). Through a combination of in-depth statistical analysis of the results arising from Amphenol’s extended tests with ground crab shell and demineralised shell, and parallel complementary testing carried out on a companion treatment unit at C-Tech, we have been able to act in an advisory capacity to our partners, steering the test programme in the light of knowledge gained, and ultimately producing recommended operational protocols for a planned larger scale pilot unit to be installed at Amphenol in the final phase of the project.
Co-funded by Innovate UK