Enzyme-based strategy for toxic waste treatment and waste minimization

The increasing amounts of pesticides used throughout the world, as well as the increasingly stringent governmental regulations concerning waste disposal, mandates improved techniques of waste disposal and minimization. In this article, parathion hydrolase, an enzyme with proven effectiveness at hydrolyzing organophosphates, was used to treat a cattle dipping liquid containing the pesticide, coumaphos, which is used to kill a disease-causing tick. Waste is generated from this process when a toxic dechlorination product of coumaphos, potasan, accumulates to concentrations hazardous to the cattle. This pesticide system was used as a model to demonstrate how enzyme technology can be applied to waste treatment and minimization. Kinetic experiments showed that the hydrolysis of the two organophosphate substrates can be modeled as first-order reactions with identical rate constants. It was further shown that the enzyme is capable of hydrolyzing only dissolved substrates. Because of the eightfold greater solubility of potasan than coumaphos (16.9 vs. 2.2 mumol/L), it was possible to utilize the enzyme to hydrolyze potasan selectively. Thus, by limiting the amount of enzyme, it is possible to remove potasan selectively to extend the lifetime of the cattle dipping liquid, thereby reducing the amount of waste generated. Based upon experimental results, a mathematical model describing the system was developed and verified. The mathematical model was then used to simulate the ability of the enzyme to hydrolyze the total amount of organophosphates, and to degrade selectively all of the toxic potasan without a significant loss of coumaphos.     

Anaerobic waste stabilization

The present knowledge of the microbiology, physiology and regulation of anaerobic digestion in conventional or advanced processes is reviewed. In all systems the carbon flow from biopolymers to biogas is determined by syntrophic interactions of fermentative or acetogenic bacteria with methanogens at the level of interspecies hydrogen transfer. Inhibitors or heavy metal ions may interfere at different levels.The stabilization of waste at mesophilic and thermophilic temperatures is compared and the process stability as well as the inactivation of pathogens is discussed. Characteristics of conventional digestion systems and of recently developed advanced processes with solids and liquids uncoupling are compared and selection criteria with respect to the type of sludge are outlined.Areas of future research for a better understanding of the biochemistry, the physiology and the regulation of the degradation of pollutants are suggested.     

Production of butanol from starch-based waste packing peanuts and agricultural waste

We examined the fermentation of starch-based packing peanuts and agricultural wastes as a source of fermentable carbohydrates using Clostridium beijerinckii BA101. Using semidefined P2 medium containing packing peanuts and agricultural wastes, instead of glucose as a carbohydrate source, we measured characteristics of the fermentation including solvent production, productivity, and yield. With starch as substrate (control), the culture produced 24.7 g l⁻¹ acetone–butanol–ethanol (ABE), while with packing peanuts it produced 21.7 g l⁻¹ total ABE with a productivity of 0.20 g l⁻¹ h⁻¹ and a solvent (ABE) yield of 0.37. Cell growth in starch, packing peanuts, and agricultural wastes medium was different, possibly due to the different nature of these substrates. Using model agricultural waste, 20.3g l⁻¹ ABE was produced; when using actual waste, 14.8 g l⁻¹ ABE was produced. The use of inexpensive substrates will increase the economic viability of the conversion of biomass to butanol, and can provide new markets for these waste streams. Journal of Industrial Microbiology & Biotechnology (2002) 29, 117–123 doi: 10.1038/sj.jim.7000285 Received 14 November 2001/ Accepted in revised form 07 June 2002     

Anaerobic digestion of animal waste: waste strength versus impact of mixing

We studied the effect of mode of mixing (biogas recirculation, impeller mixing, and slurry recirculation) and waste strength on the performance of laboratory scale digesters. The digesters were fed with 5% and 10% manure slurry, at a constant energy supply per unit volume (8 W/m3). The experiments were conducted in eight laboratory scale digesters, each having a working volume of 3.73 L, at a controlled temperature of 35+/-2 degrees C. Hydraulic retention time (HRT) was kept constant at 16.2 days, resulting in a total solids (TS) loading rate of 3.08 g/Ld and 6.2 g/Ld for 5% and 10% manure slurry feeds, respectively. Results showed that the unmixed and mixed digesters performed quite similarly when fed with 5% manure slurry and produced biogas at a rate of 0.84-0.94 L/Ld with a methane yield of 0.26-0.31 L CH4/g volatile solids (VS) loaded. This was possibly because of the low solids concentration in the case of 5% manure slurry, where mixing created by the naturally produced gas might be sufficient to provide adequate mixing. However, the effect of mixing and the mode of mixing became prominent in the case of the digesters fed with thicker manure slurry (10%). Digesters fed with 10% manure slurry and mixed by slurry recirculation, impeller, and biogas recirculation produced approximately 29%, 22% and 15% more biogas than unmixed digester, respectively. Deposition of solids inside the digesters was not observed in the case of 5% manure slurry, but it became significant in the case of 10% manure slurry. Therefore, mixing issue becomes more critical with thicker manure slurry.     

Anaerobic waste water treatment

Anaerobic waste water treatment will be employed in place of aerobic processes for many types of effluents in the near future. There is an increased understanding of the fundamentals of the process, and inexpensive high-rate treatment systems are being developed. In 1978 a full scale anaerobic upflow reactor was installed in The Netherlands and this system has since found many applications in industries all over the world. An advanced anaerobic fluid bed installation is now under construction at a bakers' yeast factory in Delft, The Netherlands.     

Nitrification of swine waste

Complete oxidation of ammonia nitrogen (approximately 1000 mg/L) to nitrite was observed in stabilized swine waste after 49 days in incubation at 400 rpm and 29 degrees C, only if 10% (v/v) activated sludge from a wastewater treatment unit and 1.5% (w/v) CaCO3, were added. Stabilized swine waste contains less than 0.09 most probable number (MPN) per millilitre of nitrosobacteria and 2.3 MPN/mL of nitrobacteria. In activated sludge, the concentrations of these bacteria were 2.4 MPN/mL for nitrosobacteria and 4.2 x 10(5) MPN/mL for nitrobacteria. In the swine waste where ammonia was oxidized to nitrite, the nitrosobacteria growth increased to 5.5 x 10(5) MPN/mL, while the nitrobacteria growth decreased to 2.3 MPN/mL. Inoculation of a freshly stabilized swine waste with 10% (v/v) of the active nitrifying waste and addition of 1.5% (w/v) CaCO3, accelerated the oxidation of ammonia nitrogen to nitrite; the reaction was completed after only 5 days of incubation. Increasing the incubation period to 10 days resulted in the complete oxidation of the accumulated nitrite to nitrate. In the stabilized swine waste, complete nitrification without accumulation of nitrite was obtained in only 5 days of incubation when the waste was inoculated with both enriched nitrifying populations (10(6)-10(7) MPN/mL).     

Managing municipal solid waste

Goal  

This research aims to assess the environmental effects of integrated strategies in a municipal waste management system. In particular, analysis is focused on a waste stream in Palermo, where landfill involves the prompt disposal of the most waste after collection. The current local management system is compared with two integrated waste management alternatives. Both the options comply with Italian regulations, but each one predicts adopting the available technologies in different ways.     

Modeling solid waste decomposition

The hydrolysis rate coefficients of sorted municipal waste were evaluated from the biochemical methane potential tests using non-linear regression. A distributed mathematical model of anaerobic digestion of rich (food) and lean (non-food) solid wastes with greatly different rates of polymer hydrolysis/acidogenesis was developed to describe the balance between the rates of hydrolysis/acidogenesis and methanogenesis. The model was calibrated using previously published experimental data [Biores. Technol. 52 (1995) 245] obtained upon various initial food waste loadings. Simulations of one- and two-stage digestion systems were carried out. The results showed that initial spatial separation of food waste and inoculum enhances methane production and waste degradation in a one-stage solid-bed digester at high waste loading. A negative effect of vigorously mixing at high waste loading reported in some papers was discussed. It was hypothesized that the initiation methanogenic centers developing in time and expanding in space under minimal mixing conditions might be a key factor for efficient anaerobic conversion of solid waste into methane.     

Webalert of waste management

Waste is unwanted or useless material. It is widely recognized that waste materials are valuable resources, whilst there is debate as to how this value is best realized. Re-use, recycling and energy recovery are being applied to regulated wastes. Yet, while recycling and re-use are increasing, the overall amounts of waste are still growing, and there is an increasing demand for primary resources and stress on eco-systems. In this webalert, we will focus on some important websites which provide readers with more informative resources related to waste management.     

Algae and waste water

Microalgal cultures offer an interesting alternative for waste water treatment (urban, industrial or agricultural effluents) because they provide a tertiary biotreatment coupled with the production of potentially valuable biomass, which can be used for several purposes. We review the main abiotic, biotic and operative factors playing a role in the cultivation of microalgae. Various types of bioreactors are scrutinized keeping in view that the main limitation upon the type of usable bioreactors is the enormous volume of water to be treated. The choice of suitable microalgae and cyanobacteria is examined in terms of productivity and easiness of harvesting. The possible alternatives to harvesting are also reviewed with an emphasis on immobilized systems. Finally, the need for more research and development is discussed.This paper was presented at the Symposium on Applied Phycology at the Fourth International Phycological Congress, Duke University.     

Accelerated food waste composting

Experiments on food waste composting under the temperate and dry conditions of Mexico City showed that the waste stabilized faster (within 2 months) if an accelerator (chopped orange peel and carrot bagasse) was used. The relatively cool and humid conditions prevailing during similar experiments in Xalapa City inhibited decomposition, and stabilization of waste, with or without accelerator, was generally slower than in Mexico City. However, addition of wood chips as a bulking agent greatly improved composting in Xalapa, leading to stabilization in just 35 days.Use of the accelerator increases the initial C/N ratio in the waste. This permits rapid utilization of any easily degradable sugars, which in turn supports rapid multiplication of mesophilic microorganisms.     

Composting of waste from palm oil mill: a sustainable waste management practice

Malaysia is blessed with abundant natural resources and bears a favorable climate for commercial cultivation of crops such as oil palm. In Malaysia the total plantation area of oil palm was 4,487,957 ha in 2008. It has been reported that in 2005 there was a total of 423 palm oil mills having production capacity of approximately 89 million tonnes of fresh fruit bunch (FFB) per year. Waste from the oil palm mill process include palm oil mill effluent (POME), generated mainly from oil extraction, washing and cleaning up processes. POME contains cellulosic material, fat, oil, and grease. Discharging untreated effluent into water streams may cause considerable environmental problems. The solid wastes generated are mainly decanter cake, empty fruit bunches, seed shells and fibre from the mesocarp. POME as well as the solid wastes may rapidly deteriorate the surrounding environment if not dealt with properly. Hence there is an urgent need for a sustainable waste management system to tackle these wastes. As these wastes are organic in origin, they are rich in plant nutrients. Composting of waste generated from palm oil mills can be good practice as it will be helpful in recycling useful plant nutrients. This review deals with various aspects of waste management practices in palm oil mills and the possibility of composting the wastes.     

Current trends in waste valorization

This paper presents the scientific breakthroughs made in bioprocess engineering and microbial biotechnology for the conversion of wastes into products with added value and/or biofuels. The significant results obtained in the emerging fields of hybrid electrosynthesis, the role of enzymes in the degradation of plastics, polyhydroxyalkanoate and 5-aminolevulinic acid production, fermentation technology and the application of molecular engineering tools to bioprocess technology are highlighted.