Abstract
The aim of this study was to evaluate if eco-friendly lubricants had an additional advantage over conventional synthetic lubricants in terms of emulsion treatment of metalworking wastewater. To these purpose, two fresh commercial synthetic cutting oil emulsions were compared with an emulsion obtained from a new cutting oil produced from the reuse of slaughtering waste (CADT-605 from Kimya Srl, Bari, Italy). The breaking of the fresh emulsions was carried out with the addition of small amounts of sulfuric acid (2–20 mL/L) followed by pH neutralization by means of calcium hydroxide. During the two-step treatments, COD, BOD5 and non-ionic surfactant (NIS) concentrations were monitored in the aqueous phase. The results demonstrated that the best results were obtained with the emulsion produced with the bio-based lubricant. In addition, this cutting oil was tested in a metalworking plant within 30 days and the resulting spent emulsion was treated with the proposed process. In all the cases, the treatment led to a drastic decrease of the COD, BOD5 and NIS contents that allow the discharge of resulting aqueous phase in sewers or in surface water bodies, together with the other wastewater produced by the plant, in agreement with the Italian regulation.
Highlights
Synthetic lubricants are a complex mixture of chemical components including olefins, paraffins, naphthenes, aromatic hydrocarbons, etc. and show low biodegradability with release of harmful compounds into the environment [1,2,3,4,5,6]
The first part of the experimental campaign was focused on the analysis of COD, BOD5 and non-ionic surfactant (NIS) of the CSE-A, CSE-B and CADT 605 emulsions after the two steps chemical treatment: after emulsion breaking and pH neutralization
A possible reuse of the precipitate, mainly constituted by calcium sulfate dehydrate with a small amount of organic compounds, as in the case of the precipitated obtained after the treatment carried out with 10-mL/L and 20-mL/L sulfuric acid (Figure 4a), may be in the production of cement for the construction industry [32]
Summary
Synthetic lubricants are a complex mixture of chemical components including olefins, paraffins, naphthenes, aromatic hydrocarbons, etc. and show low biodegradability with release of harmful compounds into the environment [1,2,3,4,5,6]. The fatty acids composition and the physical properties of these lubricants are dependent from the plant species, the climatic conditions, the soil type and the genetic variations in the plant. Animal lubricants are water insoluble and hydrophobic materials deriving from the animal fats (hard fats, i.e., stearin and soft fats, i.e., lard). The structure of these materials is based on glyceryl esters of fatty acids known as triglycerides [14,15]. The fatty acids composition and the physical properties are dependent from the animal species and the living environment. Animal lubricants are based on beef fat, clove oil, fish oil, mink oil, etc. [10,16]
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