10 12 12, 10 12 13

(UBA 2001)

Whiteware sludge and filtercake wastes are generated through the collection of waste water from the shaping (body preparation, forming, fettling, cleaning) and glazing (glaze preparation, overspray, cleaning) stages of ceramic production. This waste water contains a mixture of suspended minerals, reflecting the different raw materials used in production along with some degree of contamination. Factory wastewater typically goes to settlement tanks, before being treated with a flocculant. At this stage the material can either be disposed of as a sludge/slurry, or filtered and de-watered using a filter press, obtaining a mineral waste filtercake. Due to the lower costs of waste disposal in a solid form, most larger factories process their waste into filtercake form. The quantity of sludge or filtercake produced in a typical wall and floor tile factory ranges from 0.4 – 1.0 % of production output (European Commission, 2007).

Whilst varying from factory to factory, a typical analysis of ceramics industry ‘white sludge’ indicates the material consists of a mixture of traditional ceramic raw materials and a small amount of plaster (see composition).. Sludge or filtercake from sanitaryware production specifically is also likely to contain deflocculents typically in the form of sodium silicate, soda ash and/or sodium dispex, due to the use of a slip-casting production process.

Alongside variation between producers depending on their raw material usage, the exact composition of the waste will vary on a daily basis, derived from daily production and cleaning operations. Depending on the specific practice of the factory, body and glaze waste can either be collected in separate effluent systems or mixed together in a single system. Those factories where body and glaze waste are mixed in a single system are likely to show much greater variation in the waste composition due to the varying proportion of body : glaze waste.