Moringa flocculation : towards a low carbon wastewater management system for apparel factories

Abstract

The global apparel industry is one of the largest consumers as well as polluters of freshwater, contributing to 17% of the total industrial water contamination through the discharge of hazardous dye effluent, chemicals, detergents, and other toxins, exposing workers, communities and marine life to severe health and environmental risks. A major part of the pollution occurs downstream of the apparel industry supply chain, across millions of small unregulated apparel manufacturing factories spread across emerging economies, that lack resources to incorporate existing expensive wastewater treatment systems like membrane reactors or synthetic flocculants. With recent research identifying bio-flocculants in agroforestry and fishing industry waste streams, there lies an opportunity to develop a bottom-up wastewater management systems for small factories, ensuring on-site water contaminant removal as well as reuse of process water for multiple factory applications. Seeds from moringa oleifera, a widely cultivated tree species and cash crop in tropical climates providing multiple additional ecological benefits, has been observed to perform as effectively as synthetic flocculants in treating colored wastewater. Treated effluent can be reused for manufacturing applications as well as deployed as an effective thermal mass for collecting and distributing excess heat on the building envelope, mitigating wastewater discharge while delivering thermal comfort, air decontamination and energy capture for factory end uses. The thesis aimed to develop an integrated water management system using moringa oleifera waste as a flocculant for treating dye effluent, with Global Mamas Fair Trade Zone (GMFTZ), a fairtrade apparel factory in Ghana, as a case study. Identifying the FTZ dyeing zone as the largest source of water contaminants, the material experiments compared the dosage and efficiency of locally sourced moringa oleifera pressmeal for treating Global Mamas’ effluent containing synthetic vat dyes with effluent from a typical H&M supplier in Bangladesh and Ganga Maki Factory in India, containing reactive and natural dyes respectively. The treated effluent quality was assessed based on reductions in pH, suspended solids and color and its reusability was determined through repeated iterations of dyeing and moringa treatment. Experiments showed that approximately 2.5kg of moringa pressmeal per kL of typical dye effluent is required to remove color, moderate pH and reduce suspended solids in the effluent within recommended limits by the Ghana Environment Protection Agency. Finally, the thermal comfort benefits of circulating water across the dye workshop envelope were evaluated through mathematical analysis of potential interior temperature reduction that demonstrated a 12°C drop during the peak sun hour window in May. The experimental results coupled with lifecycle considerations demonstrated effectiveness of moringa flocculation to be greatest for natural dye-based effluent and least for Global Mamas effluent. A framework of the building-integrated moringa flocculation system was developed for Global Mamas, and various system configurations and layouts were assessed on the basis of their ease of use, thermal comfort potential, energy reduction and air quality benefits. The thesis provides an economical and bottom-up alternative for wastewater treatment and reuse in small apparel factories like Global Mamas, that can enable the transition to zero discharge and zero carbon apparel production while sustaining the local bioeconomy and protecting the ecosphere at the regional scale.