Abstract
This study investigated acid splitting wastewater (ASW) and interphase (IF) from soapstock splitting, as well as matter organic non glycerol (MONG) from glycerol processing, as potential substrates for biogas production. Batch and semicontinuous thermophilic anaerobic digestion experiments were conducted, and the substrates were preliminary treated using commercial enzymes kindly delivered by Novozymes A/C. The greatest enhancement in the batch digestion efficiency was achieved when three preparations; EversaTransform, NovoShape, and Lecitase were applied in the hydrolysis stage, which resulted in the maximum methane yields of 937 NL/kg VS and 915 NL/kg VS obtained from IF and MONG, respectively. The co-digestion of 68% ASW, 16% IF, and 16% MONG (wet weight basis) performed at an organic loading rate (OLR) of 1.5 kg VS/m3/day provided an average methane yield of 515 NLCH4/kg VSadded and a volatile solid reduction of nearly 95%. A relatively high concentration of sulfates in the feed did not significantly affect the digestion performance but resulted in an increased hydrogen sulfide concentration in the biogas with the peak of 4000 ppm.
Highlights
Poland is the seventh largest producer of rape (Brassica napus L.) with 5.2% of the total world production of this plant [1]
The amount of nitrogen was relatively low since the C/N ratio for all the investigated materials was 43–44, which was far from the 15–30 considered to be optimal for anaerobic digestion [20]
The enzymatic hydrolysis of fatty wastes from soapstock and glycerol processing performed at 50 ◦C for 24 h prior to the batch thermophilic digestion allowed a greater than twofold increase in methane yields compared to the control assays
Summary
Poland is the seventh largest producer of rape (Brassica napus L.) with 5.2% of the total world production of this plant [1]. Fatty acids react with sodium hydroxide to produce a mixture, which is separated through centrifugation into the light phase (degummed oil) and heavy phase (soapstock) The latter material accounts for 6% of treated crude oil and is the main byproduct of the refining process. It consists of free fatty acids and salts (around 60% on a dry mass basis), monoglycerides, diglycerides, triglycerides, sterols, polyalcohols, and over 50% water. It contains phosphates, because, at an earlier stage of degumming, phosphoric acid is added to the crude oil to precipitate phospholipids [2,5]. An extremely low pH of 1–2 combined with high contents of sulfates and phosphates makes this wastewater difficult to treat, and the literature dealing with biological processing of this material is scarce [7]
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