The present study deals with the comparison of different wastewater treatment plants for a company that will produce cellulose derivatives. The unit production is planned to produce pulp from poplar using BIVIS extrusion. Classically, the properties of the pulp are close to the CTMP with a saving consumption water of 86.8% which means that the concentration of the wastewater will be higher. The characterisation of the wastewater is given (TSS, COD, BOD5, N and P content) in order to compare it with the discharge limit values. Different lines of treatment are chosen according to the expected treatment performances which are 99% for the TSS, 90% for the COD, 98% for the BOD5, 68% for the N-tot content and 90% for the P-tot. The unit treatments are compared together and the choice to work with the €/ton of product enables to analyse more easily the different treatments. The investment cost is going to be considered for a period of 20 years as well as taking into account the increase of the price for the water, the electricity and the raw materials and the operating costs such as the maintenance, the repairs, etc. Considering the generated waste, two main steps of treatment are needed in order to meet the discharge limit requirements. A screening and a grit removal step as a pre-treatment enables to reduce the coarsest materials and then the physical-chemical decantation using the coagulation/flocculation is performed to remove a significant part of the suspended solids. To reduce the other pollutants, the three additional possibilities are membrane technologies which are very compact but with a high investment cost, the activated sludge which is classic in a pulp mill with a reasonable cost and a high performance, and then the aerated lagoonss which are cheap but a large space is necessary. After, the treatment for the sludge has to be done and according to the flow of the output sludge, the only suitable equipment possible is the centrifugation. At the end the cost of the investment is included in a range of 34-57€/ton of product without taking into account the fate of the sludge. Different fates are considered: landfilling, composting, agriculture applications, incineration. It increases the total cost between 20 and 70%. After discussion, a recommendation for the company to treat the wastewater is possible: a line including a screening, a grit removal, a physical-chemical decantation, an aerated sludge and a sand filter.
2014. , 60 p.