Anaerobic digestion of a mixture of cheese whey, poultry waste and cattle dung: a study of the use of adsorbents to improve digester performance

High-Solid Anaerobic Digestion: Reviewing Strategies for Increasing Reactor Performance

High-solid and solid-state anaerobic digestion are technologies capable of achieving high reactor productivity. The high organic load admissible for this type of configuration makes these technologies an ideal ally in the conversion of waste into bioenergy. However, there are still several factors associated with these technologies that result in low performance. The economic model based on a linear approach is unsustainable, and changes leading to the development of a low-carbon model with a high degree of circularity are necessary. Digestion technology may represent a key driver leading these changes but it is undeniable that the profitability of these plants needs to be increased. In the present review, the digestion process under high-solid-content configurations is analyzed and the different strategies for increasing reactor productivity that have been studied in recent years are described. Percolating reactor configurations and the use of low-cost adsorbents, nanoparticles and micro-aeration seem the most suitable approaches to increase volumetric production and reduce initial capital investment costs.

Improving performance and phosphorus content of anaerobic co-digestion of dairy manure with aloe peel waste using vermiculite

Phosphorus content of the digestate is crucial for evaluating its fertilizer utilization in anaerobic digestion system. The vermiculite containing rich-phosphorus is firstly used as an accelerant in anaerobic batch co-digestion system of aloe peel waste and dairy manure. After introducing vermiculite, the cumulative biogas production (295.14-353.96 mL/g VS), chemical oxygen demand removal rate (45.53%-71.03%), and volatile solid removal rate (50.70%-52.76%) are remarkably higher than those of reference reactor (234.08 mL/g VS, 39.38%, 45.10%). The thermal and fertility analyses manifest the digestates with vermiculite possess superior stability, admirable fertilizer values (5.97%-6.81%), and excellent total phosphorus content (11.44-13.29 g/kg). The improved co-digestion performance can be attributed to the addition of vermiculite. This work introduces a novel approach for improving the performance of anaerobic co-digestion and the fertilizer utilization of digestate in the co-digestion systems.

Treatment of cheese whey by a cross-flow anaerobic membrane bioreactor: Biological and filtration performance

Whey, produced in large quantities during cheese production, is a rapidly fermentable high strength wastewater characterized by a high biodegradability and low alkalinity. In this study, a lab-scale cross-flow anaerobic membrane bioreactor was used to address the commonly experienced difficulties such as unstable reactor performance and unexpected biomass losses when treating whey wastewater with conventional anaerobic reactors. The anaerobic membrane bioreactor provided a stable treatment performance, i.e. more than 90% chemical oxygen demand removal, and moderate membrane fluxes between 8 and 11 L m^-2 h^-1 could be obtained, applying a low cross-flow velocity of about 0.5 m s^-1. Short term critical flux tests revealed that higher fluxes up to 36 L m^-2 h^-1 are possible at elevated cross-flow velocities and/or reduced mixed liquor suspended solids concentrations. Sludge filterability indicated by capillary suction time and specific resistance to filtration deteriorated throughout the study. Chemical cleaning efficiency gradually decreased, indicating irreversible membrane fouling during long term operation.

Enhancing Anaerobic Digestion: The Effect of Carbon Conductive Materials

Anaerobic digestion is a well-known technology which has been extensively studied to improve its performance and yield biogas from substrates. The application of different types of pre-treatments has led to an increase in biogas production but also in global energy demand. However, in recent years the use of carbon conductive materials as supplement for this process has been studied resulting in an interesting way for improving the performance of anaerobic digestion without greatly affecting its energy demand. This review offers an introduction to this interesting approach and covers the different experiences performed on the use of carbon conductive materials proposing it as a feasible alternative for the production of energy from biomass, considering also the integration of anaerobic digestion and thermal valorisation.

Simultaneous addition of zero-valent iron and activated carbon on enhanced mesophilic anaerobic digestion of waste-activated sludge

The performance of biogas generation and sludge degradation was studied under different zero-valent iron/activated carbon (ZVI/AC) ratios in detail in mesophilic anaerobic digestion of sludge. A good enhancement of methane production was obtained at the 10:1 ZVI/AC ratio, and the cumulative methane production was 132.1 mL/g VS, 37.6% higher than the blank. The methane content at the 10:1 ZVI/AC ratio reached 68.8%, which was higher than the blank (55.2%) and the sludge-added AC alone (59.6%). For sludge degradation, the removal efficiencies of total chemical oxygen demand (TCOD), proteins, and polysaccharides were all the highest at the 10:1 ZVI/AC ratio. The concentration of available phosphorus (AP) decreased after anaerobic digestion process. On the other hand, the concentrations of available nitrogen (AN) and available potassium (AK) increased after the anaerobic digestion process and showed a gradually decreasing trend with increasing ZVI/AC ratio. The concentrations of AN and AK were 2303.1-4200.3 and 274.7-388.3 mg/kg, showing a potential for land utilization.

Use of biochars in anaerobic digestion

This study investigated the behavior of biochars from pyrolysis (pyrochar) and hydrothermal carbonization (hydrochar) in anaerobic digestion regarding their degradability and their effects on biogas production and ammonia inhibition. A batch fermentation experiment (42°C, 63 days) was conducted in 100mL syringes filled with 30 g inoculum, 2g biochar and four levels of total ammonium nitrogen (TAN). For pyrochar, no clear effect on biogas production was observed, whereas hydrochar increased the methane yield by 32%. This correlates with the hydrochar's larger fraction of anaerobically degradable carbon (10.4% of total carbon, pyrochar: 0.6%). Kinetic and microbiota analyses revealed that pyrochar can prevent mild ammonia inhibition (2.1 g TANk g(-1)). Stronger inhibitions (3.1-6.6 g TAN kg(-1)) were not mitigated, neither by pyrochar nor by hydrochar. Future research should pay attention to biochar-microbe interactions and the effects in continuously-fed anaerobic digesters.

Biotechnological approaches for the value addition of whey

Whey, the liquid remaining after milk fat and casein have been separated from whole milk, is one of the major disposal problems of the dairy industry, and demands simple and economical solutions. In view of the fast developments in biotechnological techniques, alternatives of treating whey by transforming lactose present in it to value added products have been actively explored. Whey can be used directly as a substrate for the growth of different microorganisms to obtain various products such as ethanol, single-cell protein, enzymes, lactic acid, citric acid, biogas and so on. In this review, a comprehensive and illustrative survey is made to elaborate the various biotechnological innovations/techniques applied for the effective utilization of whey for the production of different bioproducts.

Enhancement of biogas production from solid substrates using different techniques--a review

Biogas, a clean and renewable form of energy could very well substitute (especially in the rural sector) for conventional sources of energy (fossil fuels, oil, etc.) which are causing ecological-environmental problems and at the same time depleting at a faster rate. Despite its numerous advantages, the potential of biogas technology could not be fully harnessed or tapped as certain constraints are also associated with it. Most common among these are: the large hydraulic retention time of 30-50 days, low gas production in winter, etc. Therefore, efforts are needed to remove its various limitations so as to popularize this technology in the rural areas. Researchers have tried different techniques to enhance gas production. This paper reviews the various techniques, which could be used to enhance the gas production rate from solid substrates.

Bioconversion of poultry wastes. I--Factors influencing the assay and productivity of crude uricase by three uricolytic filamentous fungi

The optimum temperature for biomass yield and uricase production by uricolytic fungi, Aspergillus terreus, A. flavus and Trichoderma sp. was at 30 degrees C. The time required for maximum production of uricase and biomass yield was 4 days for two Aspergillus species and 6 days for Trichoderma sp. The optimum pH was at 6.4 for A. terreus and pH 6.6 for A. flavus and Trichoderma sp. The maximum fungal biomass yield was achieved in medium supplemented with 4% poultry waste. The best carbon sources for the production of uricase and mycelia yield were glycerol, sucrose and maltose by A. terreus, A. flavus and Trichoderma sp., respectively. Uric acid was found to be the best nitrogen source for production and activity of uricase by the three tested fungi. The addition of some vitamins to the culture media increased the maximum biomass yield of all the isolates, although no significantly increased uricase production was found.

Advances in poultry litter disposal technology--a review

The land disposal of waste from the poultry industry and subsequent environmental implications has stimulated interest into cleaner and more useful disposal options. The review presented here details advances in the three main alternative disposal routes for poultry litter, specifically in the last decade. Results of experimental investigations into the optimisation of composting, anaerobic digestion and direct combustion are summarised. These technologies open up increased opportunities to market the energy and nutrients in poultry litter to agricultural and non-agricultural uses. Common problems experienced by the current technologies are the existence and fate of nitrogen as ammonia, pH and temperature levels, moisture content and the economics of alternative disposal methods. Further advancement of these technologies is currently receiving increased interest, both academically and commercially. However, significant financial incentives are required to attract the agricultural industry.

Biomethanation of a mixture of salty cheese whey and poultry waste or cattle dung. A study of effect of temperature and retention time

This paper describes the results of a study aimed at improving the efficiency of anaerobic digestion of salty cheese whey in combination with poultry waste or cattle dung. Best results were obtained when salty cheese whey was mixed with poultry waste in the ratio of 7:3, or cattle dung in the ration of 1:1, both on dry weight basis giving maximum gas production of 1.2 L/L of digester/d with enriched methane content of 64% and 1.3 L/L of digester/d having methane content of 63% respectively. Various conditions such as temperature and retention time have been optimized for maximum process performance.