Effects of anaerobic digestion and additives to effluent or cattle feed on odor and odorant concentrations.

Odor intensity (5,437 observations), determined by human panelists (100 different panelists over the course of the experiment), and a number of chemical odorant concentrations were determined for manure-related samples (326) obtained from effluents from conventional stirred-tank reactor (CSTR) and fixed-film anaerobic digesters, effluents to which commercial additives or KMnO4 or H2O2 were added, and feces, urine, and mixed manure from cows fed a control or additive-containing diet. Mostly, samples were held in stoppered, Erlenmeyer flasks for 3 d at room temperature before evaluation by panelists and with chemical analyses, but shorter holding times also were tested. Anaerobic digestion reduced odor intensity linearly with increasing hydraulic retention time (HRT) up to 20 d; fixed-film digestion with 1.5- or 2.3-d HRT reduced odor intensity similarly to that observed with 10-d HRT in CSTR. Addition of commercial products and chemicals altered some odorant concentrations (e.g., ammonia) but did not reduce odor intensity; some products increased odor intensity. Addition of a commercial yeast-based product to a dairy cow diet had no detectable effect. The cow diet study showed that fresh urine and feces alone were less odorous than a mixed combination (manure). Fresh manure was less odorous than manure held for 3 d. Total phenol was the odorant most highly correlated with odor intensity. Individual and total volatile fatty acids also contributed. Ammonia did not seem to be a major contributor to odor in this data set.

Components of dairy manure management systems.

Dairy manure management systems should account for the fate of excreted nutrients that may be of environmental concern. Currently, regulatory oversight is directed primarily at the assurance of water quality; N is the most monitored element. Land application of manure at acceptable fertilizer levels to crops produced on the farm by hauling or by pumping flushed manure effluent through irrigation systems is the basis of most systems. Nutrient losses to surface and groundwaters can be avoided, and significant economic value can be obtained from manure as fertilizer if adequate crop production is possible. Dairies with insufficient crop production potential need affordable systems to concentrate manure nutrients, thereby reducing hauling costs and possibly producing a salable product. Precipitation of additional nutrients from flushed manures with sedimented solids may be possible. Composting of separated manure solids offers a possible method to stabilize solids for distribution, but, most often, solids separated from dairy manures are fibrous and low in fertility. Manure solids combined with wastes from other sources may have potential if a marketable product can be produced or if sufficient subsidy is received for processing supplementary wastes. Solutions to odor problems are needed. Energy generated from manure organic matter, via anaerobic digestion, reduces atmospheric emissions of methane and odorous compounds. Use of constructed wetlands or harvesting of photosynthetic biomass from wastewater has the potential to improve water quality, making extensive recycling possible.

Light and electron microscopic examinations of methane-producing biofilms from anaerobic fixed-bed reactors.

Ultrastructural examinations were performed on biofilms from eight anaerobic fixed-bed reactors filled with various packing materials and operated on fresh swine waste. By using light, UV, scanning, and transmission electron microscopy, the distribution of a diverse microbial population composed of bacteria and a few yeasts was determined. This is the first time that the ultrastructure of in situ anaerobic digestor biofilms has been reported. A large number of methanogenic bacteria were identified by their fluorescence under 420 nm of radiation. Of these, two morphologically distinct types were most prevalent in the films. Methanothrix spp. was present in high numbers at the film surface, whereas Methanosarcina spp. were commonly embedded in the lower regions of the film. Inhabitants of the film were surrounded by an exopolysaccharide matrix that was very dense toward the base. An extensive network of channels was observed throughout the matrix that may facilitate gas and nutrient exchange to the lower regions of the film.