Cakin, et al (2024) Designing a biochar-based pretreatment method for distillery effluents entering constructed wetlands. Journal of Cleaner Production. https://doi.org/10.1016/j.jclepro.2024.143790

Whisky distilleries generate large volumes of spent lees, a by-product of whisky production characterized by its acidic nature and high copper content. When improperly managed, spent lees can pose significant environmental risks, particularly to aquatic ecosystems. Many distilleries use constructed wetlands (CWs) to treat effluents before they are released into the environment. However, the low pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More and high dissolved copper (dissCu) concentrations in spent lees can overwhelm these wetland systems, which rely on biological organisms like plants, bacteria, and fungi. The need for an effective pretreatment method has become evident to protect these CWs from potential damage.

A promising approach to address this challenge is using biochar-based pretreatment. BiocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More, a carbon-rich material derived from organic waste, can help buffer the pH of the spent lees and remove heavy metals, such as copper, from the effluent before it enters CWs. In this study, researchers explored the potential of biochar produced from waste materials, specifically from whisky cask cooperage operations, as a sustainable pretreatment solution.

Biochar Modification and Application

To improve biochar’s efficiency, the team modified the raw biochar by treating it with sodium hydroxide (NaOH). This modification increased the biochar’s alkalinity and adsorption capacity, making it more effective in neutralizing the acidic effluent and binding dissolved copper. Two concentrations of NaOH (0.2% and 2%) were tested to optimize the biochar’s performance for real-world application in distilleries.

The study employed both batch experiments and column tests to evaluate the performance of NaOH-modified biochar. In batch tests, biochar doses of 1 g/L and 2 g/L were added to various spent lees samples to assess their ability to buffer pH and remove dissolved copper. In column tests, biochar was packed into columns to simulate continuous treatment of effluents, as would be expected in an industrial setting.

Key Findings

The results showed that NaOH-modified biochar effectively increased the pH of spent lees while removing significant amounts of dissolved copper. In the batch tests, a 2 g/L dose of NaOH-modified biochar elevated the pH from acidic levels (around 4.1-4.4) to neutral or slightly alkaline levels (pH 6.0-9.5), depending on the NaOH concentration. Additionally, copper removal rates were notable, with the biochar removing up to 5.72 mg of copper per gram in column studies.

Surface characterization techniques confirmed that copper ions were successfully adsorbed onto the biochar surface through micro-precipitation, which prevents copper from re-entering the effluent stream. This biochar-based method demonstrated similar or even superior performance to other wood-derived biochars previously reported in the literature, highlighting its efficacy as a pretreatment option.

Environmental and Industrial Benefits

This study demonstrates that biochar, particularly when modified with NaOH, can be a viable pretreatment method for distillery effluents. It not only buffers the effluent pH but also efficiently removes dissolved copper, ensuring the smooth operation of CWs. Furthermore, the use of waste-derived biochar from cooperage operations aligns with the principles of a circular economy, offering a sustainable solution to distillery waste management.

By integrating biochar into their wastewater treatment systems, distilleries can reduce their environmental impact and improve the efficiency of constructed wetlands, thereby supporting their commitment to sustainable practices. Future work will involve scaling up the process for industrial application and assessing its economic feasibility in real-world settings.

This innovative approach to managing distillery effluents could serve as a model for other industries looking to implement sustainable waste management practices.