Biosolids Samples Research Articles

Survival of fecal coliforms in dry-composting toilets.

The dry-composting toilet, which uses neither water nor sewage infrastructure, is a practical solution in areas with inadequate sewage disposal and where water is limited. These systems are becoming increasingly popular and are promoted to sanitize human excreta and to recycle them into fertilizer for nonedible plants, yet there are few data on the safety of this technology. This study analyzed fecal coliform reduction in approximately 90 prefabricated, dry-composting toilets (Sistema Integral de Reciclamiento de Desechos Orgánicos [SIRDOs]) that were installed on the U.S.-Mexico border in Ciudad Juárez, Chihuahua, Mexico. The purpose of this study was to determine fecal coliform reduction over time and the most probable method of this reduction. Biosolid waste samples were collected and analyzed at approximately 3 and 6 months and were classified based on U.S. Environmental Protection Agency standards. Results showed that class A compost (high grade) was present in only 35.8% of SIRDOs after 6 months. The primary mechanism for fecal coliform reduction was found to be desiccation rather than biodegradation. There was a significant correlation (P = 0.008) between classification rating and percent moisture categories of the biosolid samples: drier samples had a greater proportion of class A samples. Solar exposure was critical for maximal class A biosolid end products (P = 0.001). This study only addressed fecal coliforms as an indicator organism, and further research is necessary to determine the safety of composting toilets with respect to other pathogenic microorganisms, some of which are more resistant to desiccation.

Adsorption of Cadmium on Biosolids‐Amended Soils

Debate exists over the biosolid phase (organic or inorganic) responsible for the reduction in phytoavailable Cd in soils amended with biosolids as compared with soils amended with inorganic salts. To test the importance of these two phases, adsorption isotherms were developed for soil samples (nine biosolids-amended soils and their five companion controls) and two biosolids samples from five experimental sites with documented histories of biosolids application. Subsamples were treated with 0.7 M NaClO to remove organic carbon. Cadmium nitrate was added to both moist soil samples and their soil inorganic fractions (SIF) in a 0.01 M Ca(NO3)2 solution at three pH levels (6.5, 5.5, and 4.5), and equilibrated at 22 +/- 1 degrees C for at least 48 h. Isotherms of Cd adsorption for biosolids-amended soil were intermediate to the control soil and biosolids. Decreasing pH did not remove the difference between these isotherms, although adsorption of Cd decreased with decreasing pH level. Organic matter removal reduced Cd adsorption on all soils but had little influence on the observed difference between biosolids-amended and control soils. Thus, increased adsorption associated with biosolids application was not limited to the organic matter addition from biosolids; rather, the biosolids application also altered the adsorptive properties of the SIF. The greater affinity of the inorganic fraction of biosolids-amended soils to adsorb Cd suggests that the increased retention of Cd on biosolids-amended soils is independent of the added organic matter and of a persistent nature.

Quantifying Population Dynamics Based on Community Structure Fingerprints Extracted from Biosolids Samples.

This paper presents a standardized metric for quantifying the rate change in community structure of complex mixed microbial cultures such as those maintained in biological wastewater treatment systems. Quantifying the stability of microbial community structures is a first step toward more aggressive monitoring and control of biological systems for greater reliability in contaminant removal. Statistical analysis of compositions that uniquely specify the balance of populations of species in a mixed culture sample can be used to specify a biosolids community state as a unique position in an orthogonal coordinate system. Changes in biosolids state are observable as a trajectory within this coordinate space, and the rate of passage along this trajectory relates to the population dynamics. The geometric interpretation and the statistical analysis methods necessary for the proposed calculation methodology are introduced by way of simulated case studies with a simple model system. With the example of this model system, concepts of changing microbial community shape and size are contrasted. The rate change in community structure is defined geometrically in terms of a rate change in relative proportions of the characteristic community shape at constant biomass. A change in biomass is defined as the rate change in the quantity of biosolids at constant shape. The method robustness with respect to random measurement error was also demonstrated using the model system. The potential applications of the approach are presented with experimental data of microbial fatty acid compositions extracted from samples during the operation of bench-scale bioreactors degrading contaminants found in pulp mill wastewater. Scaling the level of population dynamics with a metric that is independent of chemotypic content presents a standard for direct comparisons of community responses between distinct cultures and experiments.

Intracellular dynamics of ribonucleic acid (RNA) and protein in microorganisms from periodically operated biofilters

Conventional biofilters are designed and operated as continuous flow processes where the reactors receive a constant stream of contaminated air. Recent research has shown that periodically operated biofilters can remove a greater mass of contaminants during shock loads than equally sized continuously loaded biofilters. Preliminary experiments were conducted to investigate effects of periodic operation on physiological state of biofilter microorganisms. Relative concentrations of two macromolecular components of microbial cells, RNA and protein, were quantified in biosolids samples removed from biofilters operated under different periodic and continuous loading strategies. Preliminary studies presented herein suggest that the physiological state of the microbial population present in the periodically operated biofilter differs from that of those present in the biofilter operated continuously supplied air.

Chemical Evaluation of Nutrient Supply From Fly Ash–Biosolids Mixtures

Prediction of plant nutrient supply from fly ash and biosolids (sewage sludge and poultry manure) may enhance their agricultural use as crop fertilizer. Two mild extraction methods (42‐d equilibration with ion‐exchange resins; 2‐d equilibration with pH 4.8 buffered nutrient solution) and analysis of nutrient data by the Diagnosis and Recommendation Integrated System (DRIS) were tested with 29 fly ash samples, four biosolids samples, and their mixtures. The resin method was useful for major nutrient (N, P, K, Ca, Mg, S) extraction from fly ashes and organic materials, particularly where mineralizable fractions of N and P under aerobic conditions are required. However, resins were inefficient in extracting P from high‐Fe sewage sludges because organic waste samples caused premature failure of semipermeable membranes and fouling of resins. Extraction of fly ash with dilute buffered nutrient solution was more successful because micronutrient recovery was improved, major nutrients were correlated to the resin method, both addition and removal of nutrients were recorded, DRIS analysis was possible, and equilibration was rapid (2 d). The overall nutrient supply from these extremely variable fly ashes was: (high micronutrient, low major nutrient supply). For biosolids, the major nutrients ranked: P > N ≈ Ca > S > Mg > K (sewage sludges), and N > Ca ≈ K > P > Mg > S (poultry manures). In mixtures of fly ash with 26% sewage sludge the order was: Ca > S > N > Mg > P > K, while in mixtures of fly ash and 13% poultry manure, the nutrients ranked: Ca > K ≈ N ≈ S > Mg > P. Optimal plant nutrition (especially N–P–K balancing) should be possible by mixing these three waste materials.

Effects of ultrafiltration membrane concentration and drying temperature on nutritional value of biosolids from a milk processing plant

Biosolids (sludge) from food processing plants traditionally are put into landfills or applied to land. They could be reused as animal food but have to be dewatered. Conventional dewatering methods are expensive and inefficient. Recent advancements in membrane technology could make ultrafiltration membranes a practical biosolids dewatering method used prior to conventional drying. Ultrafiltration could alter the nutritional profile of biosolids, and the temperature at which biosolids are dried can affect nutritional quality. The objective was to determine the nutritional quality of membrane concentrated biosolids dried at increasing temperatures. Biosolids samples were obtained from a milk processing plant. Part of each sample was concentrated using an ultrafiltration membrane separation system, and the remainder was unconcentrated (used as is); both samples were dried at increasing temperatures. Effects of concentration and temperature on total N, soluble N, insoluble N, organic matter, ash and available N were determined. Concentrated biosolids had higher total N (protein) and organic matter (energy) than unconcentrated. Increasing the temperature at which biosolids (both concentrated and unconcentrated) were dried increased the soluble N (protein) and available N fractions. UF membrane concentration of BS followed by conventional drying at 150–200°C resulted in BS with the highest nutritional value (highest total N, soluble N, available N and organic matter). UF membrane concentration increased the nutritional value of BS and eliminated the need for chemical coagulants and flocculents.

Fate ofCryptosporidiumoocysts,Giardiacysts, and microbial indicators during wastewater treatment and anaerobic sludge digestion

The extent of reduction in selected microorganisms was tested during both aerobic wastewater treatment and anaerobic digestion of sludge at the wastewater treatment plant in Ottawa to compare the removal of two encysted pathogenic protozoa with that of microbial indicators. Samples collected included the raw wastewater, the primary effluent, the treated wastewater, the mixed sludge, the decanted liquor, and the cake. All of the raw sewage samples were positive for Cryptosporidium oocysts and Giardia cysts, as well as for the other microorganisms tested. During aerobic wastewater treatment (excluding the anaerobic sludge digestion), Cryptosporidium and Giardia were reduced by 2.96 log10 and 1.40 log10, respectively. Clostridium perfringens spores, Clostridium perfringens total counts, somatic coliphages, and heterotrophic bacteria were reduced by approximately 0.89 log10, 0.96 log10, 1.58 log10, and 2.02 log10, respectively. All of the other microorganisms were reduced by at least 3.53 log10. Sludge samples from the plant were found to contain variable densities of microorganisms. Variability in microbial concentrations was sometimes great between samples, stressing the importance of collecting a large number of samples over a long period of time. In all cases, the bacterial concentrations in the cake (dewatered biosolids) samples were high even if reductions in numbers were observed with some bacteria. During anaerobic sludge digestion, no statistically significant reduction was observed for Clostridium perfringens, Enterococcus sp., Cryptosporidium oocysts, and Giardia cysts. A 1-2 log10 reduction was observed with fecal coliforms and heterotrophic bacteria. However, the method utilized to detect the protozoan parasites does not differentiate between viable and nonviable organisms. On the other hand, total coliforms and somatic coliphages were reduced by 0.35 log10 and 0.09 log10, respectively. These results demonstrate the relative persistence of the protozoa in sewage sludge during wastewater treatment.

Effects of different biosolids treatment systems on pathogen and pathogen indicator reduction

In this study, the effectiveness of different treatment systems in reducing pathogenic density levels was evaluated according to the criteria established by the U.S. Environmental Protection Agency municipal sludge rule (40 CFR Part 503 Rule). In a year‐long effort, wastewater and biosolids samples were analyzed for both indicator and pathogenic organisms from different existing treatment systems. The results indicate that anaerobic digestion was superior to aerobic digestion in reducing pathogen density levels under the given field conditions. Composting was far more superior to both anaerobic and aerobic digestion. This study demonstrates that the Class B requirements under the 503 Rule are reasonable and can be achievable by most existing treatment systems, whereas the Class A requirements under the same rule may not be easily achieved by many existing treatment works. The effects of volatile solids loading rates on anaerobic and aerobic digester performance were investigated. Under anaerobic digestion conditions, the log reductions in fecal coliform and fecal streptococci appeared to be dependent on volatile suspended solids (VSS) loading rates. However, this trend was not evident in aerobic digestion systems sampled. Salmonella density reductions did not appear to be dependent on VSS loading rates in either case.

Combustion—formation and emission of trace species

A diverse range of volatile organic compounds (VOCs) are emitted from wastewater biosolids processing. Odorous emissions are predominately made up of volatile sulfur compounds (VSCs) which are typically the only odorants measured. However, a range of VOCs are known to contribute to malodours yet previous studies often overlook the contribution of VOCs in comparison with VSCs. This study aims to evaluate how emissions are affected by different biosolids processing configurations, and if any non-sulfur VOCs should be included in odour measurement and management. Non-sulfur VOCs emitted from biosolids throughout six wastewater treatment plants in the Sydney, Australia region were measured at six locations on average twice each week over 2–3 weeks at each site. Variations in types of VOCs emitted throughout and between the sites were assigned to differences in WWTP processing configurations, plant operation and variations in industrial and municipal flows to the sewer network, referred to as sewer catchments. The presence of VOCs is likely due to biotic generation as well as industrial or residential additions to the sewer network. The dewatered and stored biosolids samples had the highest levels of VOC emissions. Sensorially important odorants were p-cresol and butanoic acid, based on the frequency of detection and odour activity values. Other compounds with a high risk of nuisance impacts were trimethylamine, indole and phenol emitted from the dewatered and stored biosolids, and volatile fatty acids from the anaerobic digester inlet and outlet at one particular site. The findings show that non-sulfur VOCs should be added to odorant monitoring campaigns at WWTPs. Identification of VOCs as sensorially important odorants opens opportunities for the more efficient management of nuisance odours, through targeted odour control or process improvement.