0 a stabitized disinfected quality product; a backup option for sludge disposition; and 0 dose cooperation with lqcal citizens.

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2 Part 11: A Problem Site, South Portland. Maine The South Portland facdity was plagued with difficulties from the beginning of its operation in the summer of 1982 The system experienced many failures despite the combined efforts of a conscientious staff and city engineers who continue to analyze the problems and implement corrective measures The South Portland experience clearly shows that to design and operate a composting facility with httle previous experience is to invite disaster Design The South Portland facility was designed to process 25 wet tons a day of partially dewatered wasteactivated sludge at 17% solids The sludge IS produced at the 5 5-mgd South Portland municipal wastewater treatment plant and delivered to the automated sludge composting system several miles away The operation is housed within a metal budding where automatic conveyor belt systems transport all sludge and most of the bulking materials and finished compost within the system According to specifications, sludge arrives in closed containers and is emptied into a hopper that has a drag chain bottom The drag chain conveys the sludge to a pug mill for mixing with wood chips The mixture is then conveyed to the composting area where a frontend loader picks up the mixture and constructs static pile segments 50 ft long and 10 ft high To facilitate aeration, the piles are built on top of a layer of wood chips placed over rigid, 4-in diameter, perforated schedule 80 PVC pipe Accbrding to plan, each completed pile segment is covered with a blanket of unscreened compost Each day, new pile segments are placed directly against previously constructed segments until the total 50 ft wide by 240 ft long bed is filled Oxygen and temperature monitoring probes are inserted into each plle segment as it is constructed A series of 2-hp vacuum blowers provide an adequate supply of oxygen for aerobic microbial decomposition (4000 cu fi air/hr dry ton sludge) A venting system was installed to carry compost exhaust gases, excess heat, and water vapor outside of the building where they would exhaust through a fdter pile of finished compost The system was designed so that composting would be completed m a minimum of 21 days Then the pde would be broken down and the compost muture conveyed for screening to a rotating drum covered with 3/ mesh screen The separated wood chips are conveyed to a bucket elevator and lifted into a storage silo untd they are re-used Another conveyor moves the screened compost to a separate curing area where it is held for a minimum of 30 days and then sold A septic system treats leachate and condensate from the compost pdes. all sanitary wastes generated in the budding, and equipment wash-down water The designers believed that water vapor and con- densate from the moist composting pdes would be drawn by negative aeration through the blower ducts and exhausted outside the buddmg Therefore the metal budding that houses the facdity was constructed with minimum ventllation Opera tion From the beginning the performance of the new facdity was disappointing With the onset of cold weather the facility faded completely, it was shut down throughout the winter of and again during the winter of During these emergencies the city reverted to landfilling or landspreading the sludge The problems are legion For example 0 Sludge handlmg. The sludge receiving bin is designed to hold 180 cu yd The drive mechanism for the drag chain bottom can handle only a maxlmum of 20 cu yd of sludge, provided the drag chain is moving when the sludge is dumped Operators had to install a baffle to prevent sludge from moving in the wrong direction out of the bin Sludge of more than 14% solids sticks to the drag chain and does not fall properly onto the conveyor feeding the pug mfl An 0 a stabitized disinfected quality product; a backup option for sludge disposition; and 0 dose cooperation with lqcal citizens. These key features appiy to all types of composting whether in-vessel, static aerated pile or windrow systems. Next month: The importance of working closely with citlzens in order to obtain public acceptance, and a final summary May

3 automatic conveyor belt scale (necessary to ensure that an appropriate amount of sludge feeds into the pug mill) proved inaccurate when a layer of sludge built up on the belt. The plant operator now uses a 5- gallon bucket and a bathroom scale to calculate the amount of sludge to feed to the pug mlll. 0 Wood chips handling. The wood chip unloader works well but takes 1 hour to unload a truck. Furthermore, the unloader quickly overwhelms the conveyor that carries the wood chips to the bucket elevator for loading into the storage silo. There is no mechanism to bleng new and old wood chips before storage, so new and used chips are loaded into the silo in layers. Because new and recycled chps have different moisture contents, the chip to sludge mixing ratio must change constantly as new or recycled chps are moved from the silo to the pug mu. The bucket elevator that loads the silo was originally installed out of alignment. It has since been straightened and braced with the aid of a large crane. The motor drive for the elevator is 95 feet up in the air and is very difficult to service. To simplify the handling process, new chips are now unloaded directly from incoming trucks with a live drag chain bottom onto the bituminous concrete floor of the building. These new chips are now used as base and cover for the compost pile so that they eventually get into the storage silo blended with reclaimed chips. The concrete wood chip storage silo is unheated and the wood chips in storage freeze solid as soon as winter sets in. Winter or summer the chips continually bridge within the silo. Inside the silo,. a rotating shaft mechanism (called a Flying Dutchman ) is supposed to rotate a series of chains of different lengths to break up any bridging. Instead, the chains repeatedly become tangled, and workers must risk life and limb to untangle them The belts that turn the shaft burn out about once a week A rotating mechanism, mstalled to unload the chps from the bottom of the sflo, is connected to a drive mechanism that faded unmediately when it was installed wth no clutch drive Sludge particles from the chps bulld up on the conveyor belt carrylng wood chips to the pug mdl, rendering the builtin belt scale unreliable Here the operator also uses a 5-gallon bucket and bathroom scale to determine the proper amounts of wood chips to feed to the pug mlll 0 Mixing. The pug mlll itself works very well However, metering With the onset of cold weather the facility failed completely. the proper blend of sludge and wood chips is a problem. Also, the pug mill is housed in a poorly ventilated underground concrete room, and the lime added to dewater the sludge increases the release of ammonia. Therefore, when the pug mill is operating, ammonia levels are so high that workers cannot enter the room without wearing protective masks. 0 Composting. The facility was designed to handle sludge with a 17% solids content. In practice, incoming sludge often contains only 12% solids. Therefore, a greater amount of wood chips is required to obtain the 40% solids content in the sludge/wood chips mixture that is necessary for optimum composting. With more wood chips in the mixture, more floor space than anticipated is required for adequate composting. After pile construction, composting temperatures are quickly reached. Air is pulled down through the pile under vacuum for 2 weeks and then blown positively up through the pile for 2 to 10 W &S. Exhaust gases from the composting pilas are not fed through a scrubber compost pile. At the South Portland Site there are few neighbors to complain of odors, and any bad odors that are present seem to be adequately dispersed. The top of the compost pile is covered with wood chips rather than unscreened or screened compost, as was intended. The use of unscreened compost as a cover would probably improve the uniformity of aeration and temperature. Considerable amounts of lime and ferric chloride are added to the sludge to assist dewatering by vacuum filtration. The added chemicals dilute the volatile solids content of the waste-activated sludge to between 50 and 60%. This reduced volatile solids content reduces the energy available for driving off moisture during composting. The operators believe that switching to a belt filter press would greatly improve their composting because the belt filter process uses polymer instead of lime and produces a drier (19% solids content) sludge with a higher volatile solids content (65%). 0 Screening. The damp compost mixture must be dried to 50% moisture content or less before screening to avoid severe plugging of the screen. After composting for the customary 21 to 28 days, the mixture is stdl too wet. It is standard practice now to break down the pile and spread the mixture outdoors in the sun and wind. The mixture is spread in a layer 6 to 8 inches thck on an exterior pad; for 2 or 3 days (depending on the weather) a tractor rakes and turns the sludge to dry it enough for screening. The plan now is to continue the exterior spreading, turning, and drying, even in freezing 18 Operations Forum

4 weather. (A restackmg aerated system within the building could fachtate drying and would not be affected by adverse water.) The hydraulic drive for the screen and the screen feeding conveyors were undersized and continually overheated. They have subsequently been rebuilt. The rotating screen is hexagonal, and a rotating brush cannot be used to clean it. The 1/8-in. round wire 3/4-in. mesh screen caught and held wood chips that clogged the screen regardless of the moisture content of the compost mucture. To correct ths problem, the operators lined the inside of the 3/4-in. mesh hexagonal drum with standard 3/8-in. mesh hardware cloth. The sharper finer wire of the hardware cloth effectively cleans itself, as long as the moisture content of material is less than 50%. Many other features of the screen also needed modification. 0 Marketing. The finished compost product is of good quality. The South Portland authority sells all the compost they produce at $3.50/cu yd. They could probably charge more-the nearby City of Portland successfully markets their compost at $6.00/cu yd. 0 Building. The lack of ventilation in the building caused tremendous problems. Fog has been so thick inside the building on cool sunny days that operators could not see beyond the front of the loader. When necessary, the loader operator is guided by a man with a flash light. Water vapor, condensing inside the roof, rains or snows down inside the building depending on ambient temperatures. The roof bolts and some cross members have rusted so badly that they need to be replaced. Ventilation cuts have now been made around the top of the entire building. This has decreased but not eliminated the fog. Water vapor condenses in many of the electrical conduit lines causing power failures. 0 Leachate and wastewater. The anticipated volume of compost leachate never materialized. Instead, the unanticipated volume of equipment wash-down water nearly overwhelmed the fachty's septic system. 0 Study. The City of South Portland commissioned a study of their facility to identify possible solutions for their unsolved problems. A draft report was prepared but not released m time for this paper. South Portland staff have suggested that needed improvements could be made for about $250 OOO. Lessons Learned Much can be learned from South Portland's difficult composting experiences : 0 Training and hands-on composting experience should be provided for city engineers and plant operators before plant design and operation. This will enable them to evaluate the proposed plant design before construction and operation. 0 Materials, procedures, and equipment should be thoroughly tested and proven before being incorporated into the design. Pilot tests are essential. They should include the handling of sludges and bulking agents with a variety of moisture levels and should be conducted during a full range of anticipated weather conditions. 0 Maximum operating flexibility should be incorporated into any composting fachty design. Sludge and bulking characteristics vary widely depending on their source and on operating conditions. Al component parts of any system should be able to operate independently. 0 Buildings and grounds must be big enough. Dewatered sludge often arrives wetter than predicted and designed for. Because the wet sludge requires more bulking agent and space, many facilities have been undersized. 0 Adequate ventilation is essential for any enclosed composting process. Because the composting proc- ess releases moisture into the air, the system design must provide for safe exhaust of this moisture and for off-gases hke ammonia and reduced sulfur-containing compounds. The poorly ventilated, nonrust-proof building in South Portland was unsuitable and should not be duplicated. However, a well ventilated rust-proof composting structure in Portland, Maine has caused no problems. 0 Silos for wood chip storage have generally been difficult to use because of bridging and, in cold climates, freezing. 0 For small operations use simple materials handhng equipment (that is, a front-end loader to move chps; pug mdls, mobile mixers or front-end loaders for blending sludge with bullung agent). To avoid problems with chp and sludge storage, conveyance and mixing, a small operation may need only storage bins, front-end loaders, or simple mechanical conveyors for moving the materials. 0 Allow time for phasing in any new operation. Experienced designers or operators should be present to assist during the operations shake-down period. There is always great pressure to begm operating at full design capacity, but yielding to it can mean operating chaos, dlscouraged operators, and angry citizens who may demand the premature closing of the fachty. 0 Maintain an adequate supply of back-up parts, especially for the equipment most llkely to break down. 0 Provide for alternative sludge disposal or storage in case the primary system is temporarily out of service. Back-up alternatives at South Portland included landspreading and landfihng. 0 Provide sufficient monitoring of the system so the moisture, oxygen and temperature levels throughout the composting process can be known and managed. Next month: Community Relations. C May

5 ~~ ~ 5 I um For. A For WFCF Wastewater Publication Professionals Volume 2, Number 5, May 1985 This,. C Issue Special Report on Package Treatment Systems Package treatment plants may look simple but they require as much operational skill as any wastewater system. Photo of an 8000 gal/d plant at Sutton Lake in the Gerald Freeman Recreation Area, Sutton, W Va., courtesy Carl Miller, U.S. Anny corps of Engineers. 1 0 Treatment-on-the-Spot Introducing an fsrrue on package treatm systems Package Primer Excerpts from a new WPCF Manual Practice Package Profiles From Alaska to the Middle East, packa plants solve unusual wastewater pmblams I Packages of Trouble A variety of problems hamper 6perati I6 Sludge Coxnposting-Learning from Experience Barbara Yeaman and John Walker Part N of a series on operating a compost facility looks at a problem site: South Portland, Me. Departments 4 Editorial 8 The Troubleshooter 24 Operators' Bulletin Letters 20 WPCF News Board 6 Wastewater Digest 22 Certification Quiz May