Tannery

Pre-Production Handling. Salt-cured catde hides, when received at the tannery, are individually bundled to prevent excessive moisture loss. The bundles are tied with ropes that are later cut and removed the hides may be sorted for different weight or quaUty classification at this point. It is best to have hides of similar size and thickness in a given production batch to assure an even reactivity of the processing chemicals and to avoid frequent adjustments in the machinery to compensate for size and thickness variations. In the modem large tannery, the size/quaUty classification is not necessary because the hides arrive in carload quantities under specifications as to size, type, and month of slaughter. 

Soa.king. The hides are weighed and counted into production batches. For pre-fleshed and trimmed catde hides the batches are about 3—5 t when the processing is in dmms. If the tannery has hide processors the batches may be up to 10 t. Water is added to cover the hides and allow free movement of the load. The dmm is turned intermittently during the normal 8 to 16-hour soaking period. 

The flesh and trimmings may be discarded as a waste in small tanneries. In the larger tanneries, the economies of size warrant the recovery of the fleshings for rendering or for glue or gelatin. 

Splitting. In most modem large tanneries that make upholstery leather, and in some that make shoe uppers leather, the hides are spHt in the lime condition. In splitting the hides are cut to the desired thickness with a horizontal belt knife. The hides are fed into the machine grain up. The clearance between the grain and the blade is maintained by a series of narrow rollers supported by a mbber roUer underneath the spacing roUers. The grain layer is then cut to the thickness desired to an accuracy of about 0.1 mm. 

The chrome-tanned leather is removed from the dmm and wmng to remove the absorbed tanning solution. The leather is then inspected for quaUty of the grain and other characteristics of importance for the leather being made. In large tanneries where very uniform hides are worked, the leather may be trimmed and spHt to the desired thickness. Hides spHt before tanning need no splitting at this point. 

The processing wastes come from the hides and processing chemicals. The hide wastes are the largest problem. For each metric ton of hides received at the tannery the following wastes are generated ... 

In tanneries, sodium bisulfite is used to accelerate the unhairing action of lime. It is also used as a chemical reagent ia the synthesis of surfactants (qv). Addition to alpha-olefins under radical catalyzed conditions yields sodium alkylsulfonates (wetting agents). The addition of sodium bisulfite under base-catalyzed conditions to dialkyl maleates yields the sulfosucciaates. 

Fig. 17. Pretreatment of organic wastewater on trickling filters. Industry types for which coordinates have been plotted are 1, kraft pulp and paper 2, mixed iadustry 3, wet com milling 4, dairy 5, tannery 6, meat packiag 7, food 8, pharmaceutical 9, refinery and 10, textile.

Field Investigation and Evaluation of Eand Treating Tannery Sludges, EPA/600/52-86/033, United States Environmental Protection Agency (EPA), 1986. 

Enzymes in the Tannery. The processing of skins and hides for leather (qv) has been based on enzymes ever since 1908 when Otto Rn hm patented the first standardized bate based on pancreatic enzymes (78). Leather chemistry research helped to improve understanding of the bating process, and at the same time spurred on developments to improve leather processing (79). 

Cured hides must be properly soaked to obtain satisfactory rehydration and removal of unwanted material. InterfibnUar proteins should be degraded in order to increase water uptake. Bacterial proteases and pancreatic proteases are normally preferred, and are compatible with most tannery chemicals used in soaking, ie, most surfactants and preservatives containing sodium chlorite. 

Lipids have been studied more intensively for appHcations in tanneries. Industrial Upases can be used for degreasing (80). 

Complex mixtures Tannery and Kraft mill effluent Sediment extract Sewage effluent... 

Chromium and compounds SPA Chromic acid Sodium dichromate Anodizing Cement Dyes Electroplating Paint Tanneries... 

Meat wastes S A Meat processing and preparation Abattoirs Dairies Tanneries... 

Gerb-anlage, /. tannery, -auszug, m. tanning extract. 

Gerberei, /. tanning tannery, -abfalle, m.pl. tanner s waste. 

Soda ash (sodium carbonate) is less expensive than phosphate and so tends to be used as a BW treatment in some developing countries for basic industrial processes such as mashing of farm products for animal foods, palm oil extraction, rendering plants, tanneries, and textile washing and dyeing. Often there is little or no condensate return. 

In addition, a number of small factories, including tanneries, paint and electroplating facilities, have been settled all around the inland territory. The number of residents in the hinterlands and of tourists in all the Venice area has grown constantly. The historical center of Venice (110,000 residents) still has no adequate sewage system and the connections to treatment plants have been completed only recently in the inland territory (>350,000 inhabitants). The central lagoon, where Venice is located, and the most important fresh water channels from the interior, still receive a heavy load of eutrophicating substances. 

Arsenic G S P A Arsine Arsenous acid and salts Pigment and dye Pesticide and herbicide production Metallurgical processing of other metals Glass and ceramics industries Tanneries... 

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