nd Filler Products By John V. Maxham After a sludge sample was re- New process technology boosts ceived, the consistency, ash content, Canadian Standard Freeness (CSF) amount of sludge solids recycled into raw and Bauer-McNett fiber-length dis- tribution (percent of OD solids re- paperma king materia 1s tained on 14-, 28-, 48- and 100-mesh screens) were measured. Most mills patented new process December 1992 and is now owned sent three to four sludge samples, technology can signifi- by Repap, a Canadian corporation. although some sent only one. cantly increase the total Prime Fiber, which is now de- Mill personnel collected sludge amount of sludge solids funct, held three US. patents on a samples that were representative of recycled into raw paper- process technology that converts the the sludge generated. Data were av- Amaking materials. The technology long-fiber fraction of paper mill eraged when separate samples were improves the drainage characteris- sludge into a papermaking pulp tested from a particular mill. Sludge tics of the fiber fines and clay frac- product. It successfully applied this consistency, which ranged from 16.1 tion remaining after long-fiber pulp technology at the Appleton mill percent to 48.6 percent and averaged is extracted and makes it suitable from April 1990 until August 1991. 31.6 percent, depended on the type for use as a filler in paperboard During that time, 1,922 metric tons of dewatering equipment used and products. It is estimated that 30 per- of AD market pulp was produced the type of sludge solids being de- cent of U.S. pulp and paper mills exclusively from paper mill sludge watered. Screw presses usually pro- have sludges in which the long-fiber and sold to Wisconsin Paper compa- duced the driest sludge cake, and yield is between 40 percent and 60 nies. Afterward, the company used belt presses produced a drier cake percent; the production of a filler predominantly post-consumer than either a vacuum filter or cen- product would increase the total white office wastepaper (PC-WOW) trifuge. Most of the mills that sent yield (long fiber and filler) to more as raw material to make a high- samples used belt presses. Sludges than 90 percent. brightness, low-dirt-count, 100 per- containing appreciable amounts of The technology was used in tan- cent post-consumer market pulp. biological solids and fiber fines were dem with a commercial long-fiber difficult to dewater, regardless of the recovery process in a recent study in Pulp and Paper Mill Sludge dewatering equipment used. which sludges from 33 North Amer- Characteristics and Quantities Ash content, which ranged from ican pulp and paper mills were eval- Prime Fiber initially received 2.3 percent to 55.7 percent and aver- uated. Based on that investigation, sludge samples from one Canadian aged 25.9 percent, depended on the researchers estimated that about 30 and 32 US. pulp and paper dsin- type of yrvduct the mill produced percent of the 4.2 million oven-dried terested in investigatingalternatives and the raw materials used to make (OD) metric tons of paper mill to their current disposal practices. The it. De-inking mill sludge typically sludge generated annually in the samples were tested to determine has a high ash content because its United States has sufficient pulp whether the long-fiber fraction could raw material (wastepaper)has a yield to be processed economically. be economically removed from the much higher ash content than virgin The study was conducted at the sludge and converted into a high- pulp. Coated paper mill sludge also former Prime Fiber Corp. market quality market pulp. Important has a high ash content because sig- pulp mill in Appleton, Wis., which considerationsincluded the amount nificant amounts of inorganic pig- had a nominal pulp production ca- of long fiber present as a percentage ments are added to the paper as pacity of 40 air-dried (AD) tons per of OD solids, the bleachability of the fillers or coatings. day. The mill was operated by long fiber, and the nature of the chem- The average CSF was 186, with a Prime Fiber from April 1990 until icals, dirt and debris in the sludge. range of 50 to 672. (CSF is a simple 36 March/April 1995 Experienced the most recent developments in environmental science Took a first-hand look at the newest developments in applied environmental technology Made contacts with thousands of other professionals in the environmental industry All in a single week! 88th Annual Meetin Ui Exhibition June 18th-d rd, 1995 OCIATION Technical Program More than SO6 175 sessions on air quality, waste Technical Tours San Antonio area Exhibition of the newest manufacturers and suppliers Continuing Education Courses The most comprehensive curriculum on air pollution control, waste management and environmental management, taught by leading experts in their fields For more information, please complete the coupon below and mail or fax it to: Air & Waste Management Association, ‘3ne Gateway Ceriter, Third Floor, Pittsburgh, ....................PA 15222, phone: (412) 232-3444,....................................... fax: (412) 232-3450 Please provide information about A&WMA’s 88th Annual Meeting & Exhibition, June 18-23,1995, San Antonio, Texas Name Title Affiliation Address City State/Province Postal Code Country Phone Fax IW This skid of wet lap pulp was made from paper mill sludge at the Prime Fiber plant in Appleton, Wis. test to measure the rate of water tained appreciable amounts of large cent) had an estimated long-fiber drainage from a pulp sample. The woody debris and shives that usu- yield greater than 40 percent, and higher the CSF, the greater the ally were captured on the 14-mesh five (15 percent) had a long-fiber drainage rate.) CSF varied according screen. Fiber that passed through yield greater than 50 percent. Yield to the nature of the sludge solids, the 100-mesh screen was arbitrarily is a significant factor in determining particularly the organic or volatile considered to be fine. the economics of fiber recovery fraction. High percentages of long The Bauer-McNett test showed from paper mill sludge. Research fiber and large woody debris in a that as much as 75.5 percent and as shows that if the yield is much less sludge typically yielded a high CSF little as 12.9 percent of the OD than 40 percent, it is unlikely that value, while large amounts of biolog- volatile fraction in the raw sludge fiber recovery can be economically ical solids and gelatinous fiber fines samples was retained on screens up justified, even when the recovered resulted in low CSF values. If the to 100 mesh. On average, 43.8 per- fiber quality is good. Investigators long fiber was highly refined, its free- cent of the volatile fraction was re- therefore estimated that 30 percent ness also was low. (A CSF greater tained. As little as 5.6 percent and as of U.S. mills have sludge from than 600 is high, while a value less much as 59.3 percent of the total OD which fiber recovery may be eco- than 200 is considered low.) solids was retained on screens up to nomically attractive compared to The Bauer-McNett apparatus de- 100 mesh. On average, 33 percent, other disposal alternatives. termined the size of solids con- or about one-third, of the total OD A 1991 survey conducted by the tained in the sludge samples. Screen solids was retained. National Council for Air and Stream mesh sizes 14 (1.19-millimeter open- The total percent of OD solids re- Improvement, a research organiza- ing), 28 (0.595-millimeteropening), tained on Bauer-McNett screens up tion funded by the paper industry 48 (0.297-millimeteropening) and to 100 mesh can be assumed to be to deal with environmental issues, 100 (0.149-millimeter opening) were equal to the expected yield of a shows that between 55 and 60 kilo- used to fractionate the sludge solids. sludge processing facility recovering grams of dry waste solids are gener- Those retained on the screens were long-fiber pulp from paper mill ated per metric ton of paper or pa- predominantly long fiber, along sludge. (The actual fiber yield at the perboard produced. According to with small amounts of debris and Prime Fiber mill was estimated ac- the American Paper Institute, 72.9 ash. Sludge samples from integrated curately using this assumption.) million metric tons of paper and Kraft pulp mills sometimes con- Ten of the 33 mills (about 30 per- board were produced in 1990. Using March/April 1995 37 an average of 57.5 kilograms of dry crease product quality and tonnage yield was too low to be economi- waste solids per ton as the average, while accepting poorer quality cally viable, the fiber could not be the pulp and paper industry pro- sludges. At the time, the company bleached to an acceptable brightness duced about 4.2 million OD metric was processing sludges from six or the sludge contained too much tons of waste solids that year. paper mills. dirt and debris for the screening and Table 1gives estimates of the The estimated amount of pulp cleaning system. Therefore, during total amounts of paper mill sludge, that could be produced from all six September 1991, Prime Fiber recoverable long fiber and filler gen- sources was 17.7 OD metric tons per switched from sludge to PC-WOW erated in the United States in 1990. day (19.7 AD metric tons per day), in its market pulp operations. The estimates are based on several considerably less than the 45 AD Table 3 gives the tonnage of paper assumptions: the average consis- metric tons per day hoped for.