Pre-treatment of agro-industrial wastes used as alternative nutrients for rearing Cydia pomonella

The physico-chemical and nutritional potential of starch industry wastewater (SIW), brewery wastewater (BWW) and apple pomace sludge (POM) and municipal wastewater sludge (WWS) were compared. The results showed higher nutrient content for BWW (19.52 ± 2.1 g l⁻¹ [proteins], 9.17 ± 1.5 g l⁻¹ [carbohydrates] and 0.25 ± 0.1 g l⁻¹ [lipids]) and POM (16.1 ± 1.3 g l⁻¹ [proteins], 8.2 ± 1.3 g l⁻¹ [carbohydrates] and 0.15 ± 0.2 g l⁻¹ [lipids]), and lower concentration of toxic elements (metals) for BWW (0.005 ± 0.0004 mg kg⁻¹ [Cd], 0.003 ± 0.0002 mg kg⁻¹ [Pb], 0.021 ± 0.003 mg kg⁻¹ [Al] and 1.66 ± 0.2 mg kg⁻¹ [Fe]) and POM (0.002 ± 0.0002 mg kg⁻¹ [Cd], 0.0014 ± 0.0001 mg kg⁻¹ [Pb], 0.019 ± 0.002 mg kg⁻¹ [Al] and 1.61 ± 0.2 mg kg⁻¹ [Fe]) as compared to SIW (5.1 ± 0.5 g l⁻¹ [protein], 7.5 ± 0.8 g l⁻¹ [carbohydrate], 0.13 ± 0.01 g l⁻¹ [lipid], 0.003 ± 0.0003 mg kg⁻¹ [Cd], 0.0025 ± 0.0002 mg kg⁻¹ [Pb], 0.021 ± 0.003 mg kg⁻¹ [Al] and 1.66 ± 0.2 mg kg⁻¹ [Fe]) and WWS (7.8 ± 0.9 g l⁻¹ [protein], 6.7 ± 0.7 g l⁻¹ [carbohydrate], 0.12 ± 0.01 [lipid] and 5.6 ± 0.6 mg kg⁻¹ [Cd], 138.6 ± 13.9 mg kg⁻¹ [Pb], 1758 ± 176 mg kg⁻¹ [Al] and 10782 ± 1080 mg kg⁻¹ [Fe]). To increase the nutritional potential and improve the rheological characteristics pre-treatment was carried out. Hydrolysis of BWW and POM was performed at pH (initial, neutral and alkaline-10), at different temperatures (80 °C, 100 °C and 121 °C) and time periods (15, 30, and 45 min). Hydrolysis at 100 °C for 30 min proved effective for breeding of larvae for BWW and POM wastes.

Introduction

The conversion wastewater sludge from municipalities and agro-industries into compost and value-added products (VAP) is simple and economic (Pham, Brar, Tyagi, & Surampalli, 2010). These methods are more advantageous than disposal (i.e. landfill and incineration) methods, due to their positive impacts on environment and economy (Adjalle et al., 2007; Vu, Tyagi, Valero, & Surampalli, 2009). Furthermore, agro-industrial wastes such as starch industry wastewater-(SIW), brewery wastewater-(BWW) and apple pomace sludge- (POM) are simple to treat and transform into VAPs because of their lower concentration of toxic elements and high nutrient concentration compared to municipal sludge (MS) (Brar, Verma, Tyagi, & Valero, 2007; Perron & Hébert, 2007; Vu et al., 2009). However, the lower bioavailability of nutrients is a limiting factor for the reuse of these wastes when used as alternative materials for bioconversion. In fact, waste nutrients are insoluble and trapped in a complex form in the suspended material (aggregates of organic matter, extracellular polymer, cells or cellular fragment) or adsorbed on their surface. Furthermore, hydrolysis has been used for biodegradation of organic and inorganic matter to allow solubilisation of partial nutrients and mineral waste for its use for various bio-products. The solubilisation also reduces the viscosity and particle size of the waste which increases nutrient bioavailability which is useful for the production of diets used for breeding of codling moth (CM), Cydia pomonella.

Waste pre-treatment by thermal and alkaline hydrolysis has been reported to increase biodegradability of organic matter (Chu, Lin, Lee, Chang, & Peng, 2002; Vlyssides & Karlis, 2004). According to Miron, Zêeman, Van Lier, and Lettinga (2000) and Schieder, Schneider, Bischof (2000), hydrolysis allows the conversion of less biodegradable molecules (polysaccharides, triglycerides, proteins or polyamines) by reaction with water to lower molecular weight compounds. Thermal hydrolysis leads to the mineralisation of organic elements into CO₂, H₂O and inorganic elements by reactions of oxidation and gasification (Shanableh & Jomaa, 2001).

The first objective of this study was to characterise and select the waste having best nutrient potential (proteins, carbohydrates, lipids and minerals) and physical properties (viscosity and particle size). The second objective was to improve treatment (hydrolysis) to increase nutrient bioavailability.