Microwave Radiation Influence on Dairy Waste Anaerobic Digestion in a Multi-Section Hybrid Anaerobic Reactor (M-SHAR)

Whey is a primary by-product of dairy plants, and one that is often difficult to manage. As whey processing units are costly and complicated, only 15–20% of whey is recycled for use in the food industry. The difficulties in managing waste whey are particularly pronounced for small, local dairy plants. One possible solution to this problem is to use advanced and efficient digesters. The aim of this study was to present an innovative multi-section hybrid anaerobic bioreactor (M-SHAR) design and to identify how microwave radiation heating (MRH) affects methane fermentation of liquid dairy waste (LDW) primarily composed of acid whey. The MRH reactor was found to perform better in terms of COD removal and biogas production compared with the convection-heated reactor. The heating method had a significant differentiating effect at higher organic load rates (OLRs). With OLRs ranging from 15 to 25 kgCOD∙m−3∙d−1, the M-SHAR with MRH ensured a 5% higher COD removal efficiency and 12–20% higher biogas yields.

Plant uptake of nitrogen adsorbed to biochars made from dairy manure

The conversion of dairy waste with high moisture contents to dry fertilizers may reduce environmental degradation while lowering crop production costs. We converted the solid portion of screw-pressed dairy manure into a sorbent for volatile ammonia (NH3) in the liquid fraction using pyrolysis and pre-treatment with carbon dioxide (CO2). The extractable N in manure biochar exposed to NH3 following CO2 pre-treatment reached 3.36 g N kg−1, 1260-fold greater extractable N than in untreated manure biochar. Ammonia exposure was 142-times more effective in increasing extractable N than immersing manure biochar in the liquid fraction containing dissolved ammonium. Radish and tomato grown in horticultural media with manure biochar treated with CO2 + NH3 promoted up to 35% greater plant growth (dry weight) and 36–83% greater N uptake compared to manure biochar alone. Uptake of N was similar between plants grown with wood biochar exposed to CO2 + NH3, compared to N-equivalent treatments. The available N in dairy waste in New York (NY) state, if pyrolyzed and treated with NH3 + CO2, is equivalent to 11,732–42,232 Mg N year−1, valued at 6–21.5 million USD year−1. Separated dairy manure treated with CO2 + NH3 can offset 23–82% of N fertilizer needs of NY State, while stabilizing both the solid and liquid fraction of manure for reduced environmental pollution.

A New Method to Recycle Dairy Waste for the Nutrition of Wheat Plants

Dairy products are vital components of human food, however, they are rapidly spoiled due to their high content of organic matter which encourages the growth of decomposing microbes. The recycling of dairy wastes is an ideal solution to preserve the environment, as it is in line with the principles of sustainable agriculture. In this experiment, an organic fertilizer was extracted from dairy wastes and was used for the nutrition of wheat grown on sandy soils under two-year field studies. The application rate of the extracted organic fertilizer was 8 ton ha−1. Moreover, the same rates of N, P, and K were added from inorganic fertilizers. The extracted organic fertilizer significantly (p < 0.05) enhanced the wheat growth and increased chlorophyll by 11% and 16% in the first and second season, respectively, in comparison to the inorganic fertilization. The extracted organic fertilizer significantly minimized the soil pH from an initial value of 8.00 to 7.05. The tested organic fertilizer increased the uptake of N, P, and K by 55%, 49%, and 51% above the inorganic nutrition, respectively. The wheat straw and grain yield increased by 16% and 29% as a result of the addition of the organic fertilizer extracted from dairy wastes. The dairy wastes organic fertilizer caused a notable improvement in the soil quality. The extracted organic fertilizer was able to supply wheat with its nutrient requirements as it showed a remarkable superiority over the mineral fertilization. The disposal of expired dairy waste can be managed in a way that preserves the environment by converting it to organic fertilizers. Laboratory and field experiments have proven the efficiency of the extracted organic fertilizer in nutrition of wheat plants in sandy soils with low fertility.