1975 and beyond (continued)

The requirement for paper mill liquid effluent disposal -and that from mechanical pulp mills where there are no waste process chemicals -is essentially one of solids separation by flotation and settling and then treatment to reduce Biochemical Oxygen Demand (BOD), and sometimes colour, to acceptable levels. The degree to which this effluent treatment has to be done depends largely on the nature of the receiving waters. Where these are the sea or fast-flowing rivers, as in most overseas pulp and paper producing countries, the requirements are less demanding than for situations such as exist for large Australian inland mills like APM's Maryvale mill or ANM's mill near Albury, as in both cases effluent discharge has to be made into relatively small streams with highly seasonal flows, subject to Australia's erratic rainfall. These mills have had to install exceptionally large BOD reduction facilities, that at Maryvale being an aeration tank over 100 ha in area.

In a chemical pulp mill the chemical recovery process is a major factor determining environmental acceptability as well as chemical make-up and energy costs and is the most costly part of the total pulp mill. The rotary furnace recovery process originally installed by APPM at its Burnie mill was of conservative design and relatively low efficiency compared with the rapidly developing kraft recovery process based on the Tomlinson smelter-furnace. To provide a better alternative APPM in the mid-1960s developed a version of the US Zimmermann wet oxidation process, in which organic matter in the waste pulping liquor is oxidized in the aqueous phase by air at very high pressure and temperature. APPM installed a small commercial plant in 1967,[104] the first successful such plant to operate on soda waste liquor in the world. In 1979 this was replaced with a larger plant which has operated with very high chemical and heat recovery and low environmental impact.

Another approach to chemical recovery from spent soda pulping liquor was taken by APM for use with soda-AQ pulping. It is based on the Direct Alkali Recovery System (DARS), first proposed by Toyo Pulp in Japan and further developed by APM as a fluidized bed application.[105] In this process spent liquor is burned in the presence of ferric oxide and the sodium ferrite formed reacted with water to give sodium hydroxide and ferric oxide which is recycled. The process was operated experimentally in a pilot plant at APM's Maryvale mill from 1980 to 1982 and has capital and operating cost advantages over other recovery processes. The first commercial DARS plant has been recently installed by APPM at its Burnie mill under a licensing agreement with APM.

Today, product development in the pulp and paper industry still tends to follow overseas trends, with some adaptation to meet local raw material and market needs. Highest growth in consumption in recent years has been in the printing and writing area, particularly for magazine and office and computer papers, and in a departure from its traditional business area, APM has now installed a plant to enter the latter field.

Australian Academy of Technological Sciences and Engineering