Novel treatment methods of sedimented fibre sludge, 0-fibre, for utilization

Historically, pulp mills across the boreal area have discharged large quantities of effluents with high content of wood fiber into receiving water systems. Until the 1950's, when the waste water treatment plants become more... [ view full abstract ]

Historically, pulp mills across the boreal area have discharged large quantities of effluents with high content of wood fiber into receiving water systems. Until the 1950's, when the waste water treatment plants become more common in the pulp mills, the effluents were commonly discharged into nearby waters untreated. The excess organic loading causes eutrophication and oxygen depletion in the water systems. In addition, the biogas generation from the degradation of organic matter have a negative impact on the exploitation of the area. Estimated number of old pulp mill sites holding the polluted catchment area with sedimented fibre sludge (0-fibre), vary but in 1994 the worldwide number of active pulp mills was over 9 000, and due to long history of pulp making the problem associated to 0-fibre is major and worldwide.

Näsijärvi, the adjacent waters of Tampere, was used as a receiving watercourse for sulphite pulp mill effluents almost for a century. The pulp mill and all the other industrial activities in the district of Lielahti has been closed down and the old mill area is planned to be converted into a residential area for 25 000 citizen. However, one major environmental problem which needs to be treated is approx. 1,5 million m³ of 0-fibre in the bottom of the lake Näsijärvi. The biodegradation is a problem especially during the winter when the lake remains unfrozen most of the time. During the summer the water depth in the area remains low and the odour gases e.g. ammonia, total reduced sulphur compounds (TRS) and volatile organic compounds (VOC) have negative effect on recreational activities and fishing industry in the area.

An extensive research has been done for various treatment methods for 0-fibre. Energy use applications such as gasification and combustion as well as composting for growth media material have been tested. However, the capacity for energy use and composting is limited and, therefore, mass stabilization has been tested as an alternative solution. The stabilization of 0-fibre with alkaline binders, such as fly ash or lime, increases the pH level of 0-fibre to 10-12 which is unfavourable for most of the degradating microbes (Watcharapol & Boonchai, 2014; Lohiniva et al. 2001). According to laboratory studies the gas formation can be substantially inhibited with stabilization. At least part of the 0-fibre has to be dredged to achieve sufficient water depth in the lake. Utilization of mass stabilized surplus soils and dredged 0-fibre mixture in filling material in the area and in-situ stabilization of the 0-fibre on the bottom of the lake have been discussed in this presentation.

_{Works sited:}

_{Watcharapol W. & Boonchai W., 2014, Alkaline Pretreatment of Waste Activated Sludge in Anaerobic Digestion, Journal of Clean Energy Technologies, Vol. 2}

_{Lohiniva, E., Mäkinen, T. & Sipilä, K., 2001, Lietteiden käsittely Uudet ja käytössä olevat tekniikat, VTT anouncements 2081.}