Review and evaluation of specific industrial wastewater treatment and reuse system

Publication Type:
Thesis
Issue Date:
2007
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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- Australian water demands are increasing significantly in conjunction with the increase in urbanisation and industrialisation. Water is a valuable resource, not only in Australia but also around the world; thus, there is scope to make better use of water by adopting recycling of water as an additional water resource. Water reclamation is the best sustainable solution for water crisis. The recirculation of wastewater to reusable water can be achieved by implementing specific wastewater treatment technologies for wastewater recycling for non-potable purposes. This study is based on the fibre cement industry. Fibre cement is a blend of cellulose fibre material from radiata pine tree, Portland cement, sand, water and other chemical additives. The fibre cement industry manufactures cement boards used for flooring and partition walls in different thicknesses and sizes. The manufacturing of fibre cement boards is similar to the paper and pulp industry in terms of manufacturing process, the technology involved and the equipment used in the process. Water consumption is very high, as a large amount of water is required for the preparation of consistent slurry, cleaning of the vacuum assisted rotating drum and belt (felt), cooking of boards, chemical dilution and house keeping. The study deals with the investigation of water usage, wastewater treatment and its recycle for the fibre cement industry on industrial premises. In this project, the performance of Dissolved Air Flotation (DAF) was investigated extensively. The study was carried out to enhance the performance of the DAF unit and to increase the oil recovery from the DAF unit. The study included both laboratory and field based investigations. The experimental investigations of the DAF found that the performance of the DAF was low. There were many reasons for the drop in efficiency, such as the increased volume of the condensate wastewater and the decrease in chemical doses, wear and tear of the mechanical parts. The recycle stream pressure was found to be below the recommended pressure. Jar test analyses were carried out to optimise the coagulant and flocculant doses for the DAF unit. Different sets of experimental combinations were carried out with varying coagulant dose and constant flocculant dose. The best results were found at l.2L/h flocculant dose and 2.lL/h coagulant dose. The turbidity was the lowest at this optimum condition (36 NTU) and the pH remained below the expected range (8.33). Some onsite trouble shooting activities were carried out to enhance the performance of the DAF unit, such as cleaning of the unit, replacement of Teflon scraping blades (mechanical skimmer), tuning of scraping chain, alignments of the scraping blades, tuning of recycling pressure and adjustment of air flow for the micron size air bubble generator. The investigation of effluent treatment plant (ETP) was also carried out. Water samples from different locations were collected and analysed for pH, conductivity, TSS and turbidity. Investigations showed that water usage can be lowered by using water minimisation tools and a water integration approach. Water pinching is used for water minimisation. Along with water minimisation studies, treatability studies were conducted to recycle wastewater. Two lab-scale electrocoagulation and zeolite ion exchange units were employed to reduce the conductivity from wastewater. It was found that these technologies were not efficient enough in the reduction of conductivity therefore, a theoretical study on the application of nanofiltration and electrodialysis to treat high conductivity wastewater for recycling was also conducted. Nanofiltration was found to be cheaper and more efficient for water recycling within industrial premises. In summary, the performance of dissolved air flotation was raised by implementing optimised chemical doses and the tuning of DAF unit. The removal efficiency was increased from 40% to 70%. Water recycling and reuse is an effective and good, practical solution for the growing water crisis around the world.
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