Different types of sludge granules in UASB reactors treating acidified wastewaters

Evaluation of support matrices for immobilization of anaerobic consortia for efficient carbon cycling in waste regeneration

Efficient metabolism of fatty acids during anaerobic waste digestion requires development of consortia that include "fatty acid consuming H(2) producing bacteria" and methanogenic bacteria. The objective of this research was to optimize methanogenesis from fatty acids by evaluating a variety of support matrices for use in maintaining efficient syntrophic-methanogenic consortia. Tested matrices included clays (montmorillonite and bentonite), glass beads (106 and 425-600mum), microcarriers (cytopore, cytodex, cytoline, and cultispher; conventionally employed for cultivation of mammalian cell lines), BioSep beads (powdered activated carbon), and membranes (hydrophilic; nylon, polysulfone, and hydrophobic; teflon, polypropylene). Data obtained from headspace methane (CH(4)) analyses as an indicator of anaerobic carbon cycling efficiency indicated that material surface properties were important in maintenance and functioning of the anaerobic consortia. Cytoline yielded significantly higher CH(4) than other matrices as early as in the first week of incubation. 16S rRNA gene sequence analysis from crushed cytoline matrix showed the presence of Syntrophomonas spp. (butyrate oxidizing syntrophs) and Syntrophobacter spp. (propionate oxidizing syntrophs), with Methanosaeta spp. (acetate utilizing methanogen), and Methanospirillum spp. (hydrogen utilizing methanogen) cells. It is likely that the more hydrophobic surfaces provided a suitable surface for adherence of cells of syntrophic-methanogenic consortia. Cytoline also appeared to protect entrapped consortia from air, resulting in rapid methanogenesis after aerial exposure. Our study suggests that support matrices can be used in anaerobic digestors, pre-seeded with immobilized or entrapped consortia on support matrices, and may be of value as inoculant-adsorbents to rapidly initiate or recover proper system functioning following perturbation.

Intensive aerobic bioconversion of sewage sludge and food waste into fertiliser

The aim of this research was to verify the possibility of recovering the nutrients present in sewage sludge and vegetable food waste as fertiliser after aerobic thermophilic intensive bioconversion. The process was performed in a closed reactor under controlled conditions of aeration, stirring and pH, at a temperature of 60 degrees C, after addition of a starter bacterial culture of Bacillus thermoamylovorans SW25. End product with the best fertilising properties was obtained when sewage sludge, mixed with food waste, CaCO3 and an artificial bulking agent was thermally pretreated. The content of volatile solids and organic carbon decreased from 82.8% to 62.3% and from 37.7% to 32.5% of total solids (TS) respectively, during 12 days of bioconversion. The stable organic fertiliser produced was a powder with moisture content of 5%. Furthermore, 3.4% of nitrogen, 0.4% of phosphorus and 2.9% of potassium were also present. Addition of 10-15g of this fertiliser to 1 kg of poor fertility soil increased the growth of different plants by 113-164%.

Anaerobic granular sludge and biofilm reactors

The long retention time of the active biomass in the high-rate anaerobic digesters is the key factor for the successful application of the high rate anaerobic wastewater treatment. The long solids retention time is achieved due to the specific reactor configuration and it is enhanced by the immobilization of the biomass, which forms static biofilms, particle-supported biofilms, or granules depending on the reactor's operational conditions. The advantages of the high-rate anaerobic digestion over the conventional aerobic wastewater treatment methods has created a clear trend for the change of the role of the anaerobic digestion in the wastewater treatment plants from a pre-treatment method to the main biological treatment method. The application of staged high-rate anaerobic digesters has shown the larger potential among the recent developments in this direction. The most common high-rate anaerobic treatment systems based on anaerobic granular sludge and biofilm are described in this chapter. Emphasis is given to a) the Up-flow Anaerobic Sludge Blanket (UASB) systems, b) the main characteristics of the anaerobic granular sludge, and c) the factors that control the granulation process. Finally, the most innovative staged anaerobic digesters are also presented.