Bosgraaf, R.R., Marchek, K.A., Siemens Water Technologies, Holland(free)
This paper presents the J-Vap Process, a filter press dewatering/vacuum drying technology and its application as a biosolids dewatering and drying process at the City of Chattanooga (Tennessee, USA), Moccasin Bend WWTP. The City had been operating eight conventional recessed plate filter presses, conditioning solids with lime and ferric chloride prior to filtration, producing a Class B biosolid and had wanted to upgrade the operation to produce a Class A biosolid (as defined by the USA EPA in 40 CFR part 503B) for beneficial reuse. The City considered two different technology approaches, a filter press dewatering/vacuum drying system and centrifuges followed by thermal drying equipment. Based upon their evaluation, the filter press dewatering/vacuum drying system was chosen as the solution that best met their technical and commercial requirements.
Siemens J-Vap System was eventually selected, offering key benefits to the City with respect to lower operating temperatures for operator safety, reduced risk of combustion of the dried product, no air emissions from the drying process requiring scrubbing, overall energy efficiency and reuse of existing infrastructure. During the installation and start up of the 6 – 2M x 2M J-Vap filter presses, a component failure triggered a redesign of the J-Vap heating plate which improved the energy efficiency even further over the original design. Now operating at full capacity since July of 2009 the system has a rated capacity of over 10,000 tonnes per year dry solids based upon processing Waste Activated Sludge (WAS) only. In practice the City has been processing a combination of WAS and primary sludge obtaining throughputs almost 2 times the rated capacity. Through the data collected during more than 200 operating cycles during field performance trials and operational information from the City’s operator logs this paper will demonstrate that the J-Vap System uses substantially less energy than conventional thermal drying systems for every kilogram of water removed, operating at maximum temperatures below 82°C.
Although the City is still disposing of the material as it were a Class B biosolid, they have embarked on a program to have the material classified as a Class A EQ quality biosolid to broaden its options for beneficial reuse.
Biosolids, Class A, beneficial reuse, drying, vacuum drying, filtration, J-Vap