Inhibition of anaerobic digestion process: A review

The uncontrolled discharge of large amounts of food waste (FW) causes severe environmental pollution in many countries. Within different possible treatment routes, anaerobic digestion (AD) of FW into biogas, is a proven and effective solution for FW treatment and valorization. The present paper reviews the characteristics of FW, the principles of AD, the process parameters, and two approaches (pretreatment and co-digestion) for enhancing AD of food waste. Among the successive digestion reactions, hydrolysis is considered to be the rate-limiting step. To enhance the performance of AD, several physical, thermo-chemical, biological or combined pretreatments are reviewed. Moreover, a promising way for improving the performance of AD is the co-digestion of FW with other organic substrates, as confirmed by numerous studies, where a higher buffer capacity and an optimum nutrient balance enhance the biogas/methane yields of the co-digestion system.

Reviewing the anaerobic digestion of food waste for biogas production

Recent advances in lactic acid production by microbial fermentation processes

Toxicants inhibiting anaerobic digestion: a review.

Food wastage and its accumulation are becoming a critical problem around the globe due to continuous increase of the world population. The exponential growth in food waste is imposing serious threats to our society like environmental pollution, health risk, and scarcity of dumping land. There is an urgent need to take appropriate measures to reduce food waste burden by adopting standard management practices. Currently, various kinds of approaches are investigated in waste food processing and management for societal benefits and applications. Anaerobic digestion approach has appeared as one of the most ecofriendly and promising solutions for food wastes management, energy, and nutrient production, which can contribute to world’s ever-increasing energy requirements. Here, we have briefly described and explored the different aspects of anaerobic biodegrading approaches for food waste, effects of cosubstrates, effect of environmental factors, contribution of microbial population, and available computational resources for food waste management researches.

/pdf/food-waste-to-energy-an-overview-of-sustainable-approaches-3ko11gyhs5.pdf

Food Waste to Energy: An Overview of Sustainable Approaches for Food Waste Management and Nutrient Recycling

A whey solution was used as a substrate for methane production in an anaerobic fixed-bed reactor. At a hydraulic retention time of 10 days, equivalent to a space loading of 3.3 kg (m3 day)−1, 90% of the chemical oxygen demand was converted to biogas. Only a little propionate remained in the effluent. Toxicity tests with either copper chloride, zinc chloride or nickel chloride were performed on effluent from the reactor. Fifty per cent inhibition of methanogenesis was observed in the presence of ≥10 mg CuCl2 l−1≥40 mg ZnCl2 l−1 and ≥60 mg NiCl2 l−1, respectively. After exposure to Cu2+, Zn2+ or Ni2+ ions for 12 days, complete recovery of methanogenesis by equimolar sulfide addition was possible upon prolonged incubation. Recovery failed, however, for copper chloride concentrations ≥40 mg l−1. If the sulfide was added simultaneously with the three heavy metal salts, methanogenesis was only slightly retarded and the same amount of methane as in non-inhibited controls was reached either 1 day (40 mg ZnCl2 l−1) or 2 days later (10 mg CuCl2 l−1). Up to 60 mg NiCl2 l−1 had no effect if sulfide was present. Sulfide presumably precipitated the heavy metals as metal sulfides and by this means prevented heavy metal toxicity.

Inhibition of methane production from whey by heavy metals--protective effect of sulfide.

Salt whey permeate was used as a substrate for lactic acid production by different strains of homofermentative lactobacilli. An isolate from Egyptian Cheddar cheese proved to be the most effective lactic acid producer. The salt whey permeate was optimized by addition of yeast extract and minerals to enable exponential growth of organisms. The lactic acid productivity of free and immobilized cells was compared and fermentation conditions were improved. Continuous lactic acid fermentation from salt whey permeate with cells immobilized in agarose beads was successfully carried out in a chemostat with a steady lactic acid concentration of 33.4 mg/ml.

Batch and continuous production of lactic acid from salt whey using free and immobilized cultures of lactobacilli

The aim of this work was to remove nitrate-N and organic pollutants from wastewater of the dairy industry by denitrification. An artificially prepared wastewater, containing 250 mg/l nitrate-N and 1.5 g/l whey powder, was completely denitrified with removal of 90%–93% of the chemical oxygen demand (COD) of the whey powder by suspended or immobilized mixed cultures and by a suspended or immobilized pure culture that was isolated from the mixed culture inoculum. For the above COD/nitrate-N ratio of 6:1, the results indicated that the organic compounds of the wastewater served as electron donors for complete denitrification and that there was no need to add an external carbon source. In batch denitrification assays the suspended or immobilized mixed cultures proved to be more active and reacted faster than the isolated pure cultures. In continuous denitrification processes with immobilized pure or mixed cultures, the alginate beads, used for immobilization, were not stable for more than 12 days of incubation. The mixed free cultures removed the nitrate-N and COD continuously with no change of their activity for at least 15 days at an optimum hydraulic retention time of 0.27 days with a loading rate of 900 mg nitrate-N l−1 day−1.

Removal of organic pollutants and of nitrate from wastewater from the dairy industry by denitrification

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Inhibition of methane production from whey by heavy metals--protective effect of sulfide.

Batch and continuous production of lactic acid from salt whey using free and immobilized cultures of lactobacilli

Removal of organic pollutants and of nitrate from wastewater from the dairy industry by denitrification