Methanol in the pulp and paper industry has been a source of concern for many years. Methanol and other chemicals called Hazardous Air Pollutants, or HAPs, are produced in the paper making process and get dissolved in the wastewater where they have to be treated before the wastewater effluent can be sent to the mill’s receiving stream. There are several sources within the paper making process that produce a highly concentrated volume of methanol, these sources include digester and evaporator condensates, white water from screening, cleaning and thickening, bleach plant washer filtrates, and paper machine white water. The most highly concentrated streams of methanol and other HAPs come from the condensates of the Kraft area, commonly referred to as foul condensates or combined condensates. If these pollutants are not pre-treated, they can frequently cause air pollution problems by these highly volatile compounds.
Treatment of HAPs in paper mills are usually accomplished by steam stripping the foul condensates, or by “hard –piping” the condensate to a biological treatment system, usually an ASB or activated sludge system. Since the Cluster Rules from the Clean Air Act Amendments of 1990 that required the collection and treatment of foul condensates to reduce the pollution to both air and water, the majority of paper mills have installed steam strippers. However, there are many mills that employ the “hard-piping” option under the 1998 MACT I rule. This option mandates that the condensates be collected and transported through an enclosed piping system to a biological treatment unit (an ASB or activated sludge system) and introduced below the surface of the water. Many times, the condensates from the “hard-pipe” enter the ASB or activated sludge system in close proximity with the mill wastewater, so these two sources can become well mixed and aerobic biological treatment can begin. Since methanol is easily degraded by the bacteria in a treatment system, it is generally reduced to acceptable limits very quickly as long as the eight growth pressures for biological activity are met. If there are problems associated with the degradation across a system, nutrient supplementation, and/or wastewater bioaugmentation are generally employed to further degrade the methanol and other HAPs.