Daryl McCartney

Sulfide inhibition of anaerobic degradation of lactate and acetate

Abstract Bench-scale batch anaerobic degradation of lactate and acetate was investigated using three sets of serum bottles. All serum bottles were fed 1g 1−1 COD and 15.6 mM (1.5 g 1−1) SO42− at the start of the experiment. Set one (SL) used lactic acid, set two (SA) used acetic acid, and set three (SM) used a 1:1 mixture on a COD basis of the two organic acids. Each set consisted of 10 serum bottles of which 5 were started at a pH of 7 and 5 at a pH of 8. Each pH subset reactor had a different initial total sulfide (TS) concentration, which varied from 3.13 to 31.3 mM (100–1000 mg 1−1). Acetate removal followed first order reaction kinetics and proceeded without any significant sulfate reduction. Inhibition of acetate removal by aqueous hydrogen sulfide (H2S) was modeled using an exponential function. Both propionate removal and sulfate reduction were inhibited proportionally to the concentration of TS. This suggests a crucial role for the sulfate reducing bacteria in mediating propionate degradation to acetate. In the low pH subset of SM, complete inhibition of sulfate reduction occurred at only 17% inhibition of methanogenesis. Complete COD removal occurred in all the serum bottles of the high pH subsets, indicating the important role of H2S in sulfide inhibition.

A review of the effectiveness of current time–temperature regulations on pathogen inactivation during composting

Pathogenic organisms can be present in all types of compost feedstocks. Since the infective dose for many of these organisms is very low, it is generally accepted that pathogens should be reduced t...

Determining the Critical Bulking Agent Requirement For Municipal Biosolids Composting

Air space within municipal biosolids composting feedstock is an important design and operating consideration. Bulking agents, such as woodchips, are required to ensure adequate air space levels are maintained. The purpose of the study was to report on the use of bench-scale air space tests to identify the critical bulking agent requirement (CBAR). CBAR was defined as the minimum amount of bulking agent required to maintain adequate pore space oxygen levels. Bench-scale air space tests were correlated to full-scale windrow composting performance, particularly pore space oxygen levels. Four volumetric ratios of municipal biosolids and woodchips were tested ranging from 1:1 to 1:4 (biosolids:wood-chips). The traditional soil physics methodology was used to determine total air space (TAS). A new step was added to the method which allowed one to also determine the free air space (FAS) within the sample. In addition, the effect of compaction on TAS and FAS was also investigated. Windrows were monitored for pile temperature and pore space oxygen concentration. At the end of the run, maturity, fecal coliform density, and the presence of salmonella were determined. The heavy metal content of the feedstock material, finished compost, and recycled woodchips were also determined. For the materials tested, biosolids and woodchips, the CBARs, to achieve a FAS of ≥20% and a minimum pore space oxygen content of ≥5%, were estimated as 1:2.5 and 1:2.8 (biosolids:woodchips; vol:vol), respectively. Assuming a target pore space oxygen level of > 5%, the recommended air space value depended on the test method used, and ranged from 26 to 61%. Bench-scale air space values were found to correlate to windrow pore space oxygen levels and operating temperature. A significant thermophilic period was not observed in any of the recipes tested. It was speculated this was caused by the coarse particle size of the woodchips. Based on the observations of the metal contents of the materials used in this investigation, the metal content of recycled material should be considered when evaluating the advantages and disadvantages of using recycled woodchips as a bulking agent.

Effects of pH on sulfide toxicity to anaerobic processes

Abstract Effects of sulfide on anaerobic degradation of lactate, butyrate, propionate (Pr) and acetate (Ac) were studied in batch serum bottles. Maintenance of higher pH = 7.7–7.9 allowed for tolerance of much higher concentrations of sulfide pointing to un‐ionized H2S as the inhibitory sulfide species. Concentration thresholds of 50% inhibition by total and un‐ionized sulfide were determined. Lactate utilization was the least affected while propionate degradation was the most affected by sulfide. Data analysis using semi‐log graphs of substrate utilization rates vs. sulfide produced retardation coefficients (k) of 0.6 L mg−1 for acetate and 1.2 L mg−1 for propionate. Retardation was more pronounced in a mixed Ac/Pr run than in pure Ac and Pr runs.

Effect of C:N Ratio on Microbial Activity and N Retention: Bench-scale Study Using Pulp and Paper Biosolids

The effect of C:N ratio on the performance of bench-scale composting systems treating pulp and paper biosolids was investigated. The biosolids used were obtained from the Pine Falls Paper Company located in Manitoba. The biosolids, on a wet basis, consisted of 41% primary biosolids, 21% secondary biosolids, and 39% deinking plant sludge. The biosolids were mixed with bark to achieve an initial moisture content of 60%, resulting in a recipe consisting of 1.09 kg of bark per kg of biosolids on a dry basis. Four reactors (treatments) were run with C:N ratios of 107 (control; no N supplement), 55, 29, and 18. Each treatment was replicated three times. Sulfur coated urea was used as the N supplement. Parameters monitored included C:N ratio, N recovery, material compaction, temperature, qualitative odor observations, and volatile solids reduction. The relative microbial activity was observed in-directly using volatile solids removal and the relative heat generation data. The data showed a strong negative linear relationship between C:N ratio and relative heat generation (r2=0.98) and between C:N ratio and volatile solids removal (r2=0.84 for all four treatments; and r2=1.0 for C:N = 29 to 107). The data also showed a strong nonlinear relation between N retention and C:N ratio (% retention = 101(1-0.92C:N); r2 = 0.71; n = 12). Qualitative odor observations and N losses suggested that a C:N ratio of 18 was too low, therefore a performance comparison was made between the C:N-107 and the C:N-29 treatments. It was observed that the mean volatile solids removal was 28.6% higher in the C:N-29 treatments as compared to the C:N-107 control. While this difference is significant from a bench-scale perspective, the authors question the practical significance of the difference and recommend further investigation.

Designing sustainable development indicators: analysis for a case utility

Purpose – The purpose of this paper is to present and analyze a case study on the design of a system of sustainable development indicators for an electric utility.Design/methodology/approach – The case study is based on collaboration with an electric utility and consultation with external experts. A six‐step process was used to create the indicators: conduct a needs assessment; conduct process planning; develop a draft set of indicators; test and adjust the indicators; implement the indicators; and review and improve the indicators.Findings – The case study demonstrates how existing projects impact the process of developing indicators. It highlights that any system of indicators must be linked to the business planning process. It shows how this may be accomplished through a design based on a hierarchical approach that also illustrates linkages between the indicators and incorporates existing measures.Research limitations/implications – The first three steps of the indicator design process have been comple...

Compost stability and maturity evaluation — a literature reviewA paper submitted to the Journal of Environmental Engineering and Science.

Finished compost should be both stable (resistant to decomposition) and mature (ready for a particular end-use) so that it can safely be packaged and transported, and not cause adverse effects during its end use. A variety of methods for evaluating stability and maturity are available; this paper contains a review of the effectiveness of a number of the most commonly used tests, to determine the most reliable approach(es). In the literature reviewed, it was generally agreed that a single, stand-alone test for both compost stability and maturity does not yet exist; therefore, it is best to use a combination of tests. However, there is disagreement in the literature as to what the best combination for evaluation should be, and guidelines and regulations around the world employ a variety of approaches.

Using a Biocell to Measure Effect of Compressive Settlement on Free Air Space and Microbial Activity In Windrow Composting

This paper describes the first equipment developed to include compressive loads in a physical model of the composting environment. This new type of composting reactor was named a biological load cell, or biocell for short. Our hypothesis was that the exclusion of compressive settlement in existing physical models may lead to errors if the data is used to design full-scale windrow composting facilities. Municipal biosolids were mixed with three organic amendments (wood chips, straw, and leaves) to yield mixture moisture contents of 55%. Compressive settlement analyses were completed by subjecting the mixtures to loads of 0, 4.3, 8.6, and 12.9 kPa using biocells. The effect of compressive settlement on microbial activity was investigated using the biosolids:leaf mixture under loaded (12.9 kPa) and unloaded conditions. The settlement behavior of all three mixtures was found to fit established soil compaction equations and new equations were developed to represent the vertical free air space (FAS) and bulk density profiles in composting systems. The FAS profiles indicated that existing physical models do not simulate the FAS conditions within a composting matrix and significant differences in microbial activity were observed between loaded and unloaded biocells. The microbial activity differences were attributed to the reduced FAS within the loaded biocells, which, in consequence, lead to lower pore space oxygen concentrations. It proved difficult, however, to simulate the air flow regime within a windrow composting matrix. To further develop the biocells, there is a need to investigate the in-situ stress conditions and natural draft ventilation rates of full-scale windrow systems. While further work is required to perfect the biocells as a physical model of the windrow composting environment, it has demonstrated its potential use for FAS analysis and as a standard bulk density apparatus. Using biocells, it is recommended that FAS curves be developed for a wide range of feedstock recipes. The biocell apparatus could also be developed as a standard bulk density test apparatus. Other important conclusions drawn from the work include: leaves should not be used as a bulking agent; wood chips showed superior bulking properties and are recommended for use in very high (3.7 m) windrows; straw showed intermediate bulking properties and should not be used for high windrows without further investigation; for all materials, compaction occurred rapidly after each incremental load, suggesting that windrow turning will do little to alleviate a low FAS problem associated with an incorrect composting recipe.

Development of a Rapid Moisture Content Method For Compost Materials

One of the most important design and operating parameters at composting facilities is moisture content. Existing standard gravimetric oven methods required a minimum of 19 hours to complete. In this study, by reducing the amount of sample, the time required to complete a standard gravimetric oven method was reduced to nine hours. A new infrared moisture balance method was also developed that reduced the analysis time to 33 minutes. The new infrared method, however, requires one apparatus for each result. The relative precision of the new infrared method was compared to two standard methods using five different materials: straw, celery, paper industry biosolids, municipal biosolids, and cured municipal compost. The new infrared method gave equivalent accuracy on all the materials tested, except for the low moisture content (five percent) material (straw).

Challenges in implementing a functional ISO 14001 environmental management system

Purpose – The purpose of this paper is to present the key findings of a colloquium on ISO 14001. The colloquium focused on three key areas: critical loops and synergies among management system elements, the full spectrum of management system auditing, and integrating management systems.Design/methodology/approach – A total of 40 Canadian experts on environmental management systems from a wide variety of sectors participated in the colloquium.Findings – The colloquium provided insights into implementation issues around the three key areas noted above. The colloquium focused on discussing issues associated with corrective and preventive action, objectives and targets, internal and external auditing, and integrating change into management systems. The issues are presented in detail in the paper.Originality/value – The participants in the colloquium believed that the findings will be of interest to both practitioners and academics in environmental management systems. The findings will also be of interest to p...