# Biological Importance of Cotton By-Products Relative to Chemical Constituents of the Cotton Plant
## 3 Cotton Industry and Processing
### Cotton Waste  
Cotton by-products have provided producers with additional value, mainly in the form of livestock feed supplements and soil amendments [6; 66]. Despite its abundance, field trash is generally viewed as having little value-added potential and is, therefore, not a resource that is utilised in standard farming practices. Field trash is currently slashed and left in the field where it provides some benefits through improving soil carbon and reducing soil erosion. The high cost associated with harvesting field trash for other uses is considered a major economic hurdle.  
Cotton seeds constitute 55% of the total pinned cotton by weight, whereas cotton fibre and CGT make up about 35%-40% and 10% respectively [67]. Although historically viewed as a waste by-product of cotton processing, cotton seed is now considered a high value co-product and an important part of the cotton processing value chain. Cotton seed is fractionated into high value oils and high protein meals, both with applications in food and feed industries. In contrast, CGT is considered a lower value waste with little value adding potential and the management of CGT is  
Figure 1: Flowchart of cotton processing from field to cotton gin products.  
regarded as a financial burden to most ginning operations. CGT is generally disposed of in one of four ways: as solid waste (landfilling), composing and land application, incineration and, to a lesser extent, fed to livestock as a supplement [9; 10]. Moreover, disposal options are tightly regulated by local environmental laws which add further restrictions.  
CGT has a reasonable nutritional profile composed of dry matter (90%), crude protein (12%), total digestible nutrients (47%), calcium (11%), sodium (121 ppm), and iron (963 ppm) [66], and has been proven to contribute to the wellbeing of livestock [6; 12]. Despite this, its use has been discouraged (and banned altogether in some countries) owing to the presence of residual chemicals which are used during cultivation [68]. This has resulted in CGT being widely used as fertilizer supplements [69; 70] and compostos to maintain/conserve soil moisture and composition that improve crop production [71; 72].  
Waste generated from cotton harvesting and cotton ginning mills are used as replacement components for inorganic-based filler materials and additives, for the production of thermoplastic composites poly(lactic acid) (PLA) and low-density polyethylene (LDPE) [73]. By-products from the cotton industry have also been processed to produce fulvic acid and silica [74]. Cotton trash has been investigated in numerous studies as a renewable feedstock in bioethanol production [15; 16; 75; 76]. CGT is well suited as a biofuel feedstock because its composition has the attribute of high polysaccharide content (up to 50%) for effective and scalable conversion to biofuels.  
A promising, yet less well documented use of CGT is in the manufacturing of biologically active compounds. There are a variety of chemical compounds which occur naturally in cotton plants with wide ranging activities. Given that such compounds are present in the cotton plant, it is plausible that the remaining trash also contains a proportion of biologically active molecules. These compounds and their uses are examined and discussed in the following sections of this review.