Biokinetic analyses of adaptation and succession: microbial activity in composting municipal sewage sludge

The interactions between temperature and the microbial communities in composting municipal sewage sludge were studied to determine the optimal temperature range for efficient decomposition (stabilization) of the sludge. Information concerning thermophilic successions in such communities was also obtained. Samples were taken from several different temperature areas in a production-scale composting pile throughout the 19-day processing run. Optimum temperatures for microbial activity, determined as the rate of [14C]acetate incorporation into microbial lipids, were determined for each sample. Biomass was determined from the lipid phosphate content of the sample. Maximal activities were generally found in samples coming from lower-temperature areas (25 to 45 degrees C), whereas samples from high temperatures (55 to 74 degrees C) usually had relatively little activity. The temperature giving the optimum activity in samples incubated at a variety of temperatures during the assay tended to increase as the composting time progressed, but never exceeded about 50 degrees C. Many of these temperature response curves were similar in nature to curves reported for purified enzyme systems and pure cultures of bacteria. Comparisons of the apparent energies of activation calculated for different temperature ranges over time also indicated that the overall community was better adapted to higher temperatures during the latter part of the composting run. It was also found that the relationship between the apparent energies of activation and the apparent energies of inactivation (apparent heats of denaturation) consistently changed with sample temperature throughout the composting run, suggesting that the microbial communities from hotter samples were better adapted to high temperatures than those from cooler samples, and vice versa.(ABSTRACT TRUNCATED AT 250 WORDS)     

On the fate of LAS, NPEOs and DEHP in municipal sewage sludge during composting

The fate of hydrophobic xenobiotic pollutants such as linear alkylbenzene sulfonates (LAS), nonylphenol ethoxylates (NPEO) and di-ethyl-hexyl phthalate (DEHP) during sewage sludge composting was addressed in this work. The experiments were conducted in a fully automated in-vessel autothermal composting system which was fed with a mixture of primary and secondary sludge and manure. The mixture composition was determined to achieve satisfactory humidity, C/N ratio and free air space (FAS). The effect of various parameters, such as the initial xenobiotic concentration, the presence of multiple xenobiotic compounds and the temperature of composting material sustained during the process on the xenobiotics biodegradation kinetics was investigated. It was generally established that significant xenobiotic reduction is achievable through composting under all conditions tested. According to the obtained results, the presence of LAS, NPEO and DEHP even at higher concentrations was not inhibitory to the bioprocess. However, the presence of multiple xenobiotic compounds such as NPEO, NP and DEHP in the sludge can influence LAS removal during LAS composting.     

Biokinetic analyses of adaptation and succession: microbial activity in composting municipal sewage sludge.

The interactions between temperature and the microbial communities in composting municipal sewage sludge were studied to determine the optimal temperature range for efficient decomposition (stabilization) of the sludge. Information concerning thermophilic successions in such communities was also obtained. Samples were taken from several different temperature areas in a production-scale composting pile throughout the 19-day processing run. Optimum temperatures for microbial activity, determined as the rate of [14C]acetate incorporation into microbial lipids, were determined for each sample. Biomass was determined from the lipid phosphate content of the sample. Maximal activities were generally found in samples coming from lower-temperature areas (25 to 45 degrees C), whereas samples from high temperatures (55 to 74 degrees C) usually had relatively little activity. The temperature giving the optimum activity in samples incubated at a variety of temperatures during the assay tended to increase as the composting time progressed, but never exceeded about 50 degrees C. Many of these temperature response curves were similar in nature to curves reported for purified enzyme systems and pure cultures of bacteria. Comparisons of the apparent energies of activation calculated for different temperature ranges over time also indicated that the overall community was better adapted to higher temperatures during the latter part of the composting run. It was also found that the relationship between the apparent energies of activation and the apparent energies of inactivation (apparent heats of denaturation) consistently changed with sample temperature throughout the composting run, suggesting that the microbial communities from hotter samples were better adapted to high temperatures than those from cooler samples, and vice versa.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oxygen diffusion and microbial activity in the composting of dehydrated sewage sludge cakes

The effective diffusivity for oxygen within sewage sludge cakes was measured, and in turn used for the study of microbial activity in the sludge cake composting. The diffusivity was found to be proportional to the one and a half power of the sludge cake porosity. Composting experiments were done using two types of sludge cakes, 5 mesh sieved and pelletized. It was found that the microbial activity in the inner core region of the pelletized sludge cake was significantly less than that in the outer region, even through the rate of oxygen diffusion was fast enough to support the microorganisms' activities. It appears, therefore, that microorganisms acting to degrade organic matter grow primarily on the macroscopic interface between solids and air.     

Effect of seeding during thermophilic composting of sewage sludge

The effect of seeding on the thermophilic composting of sewage sludge was examined by measuring the changes in CO2 evolution rates and microbial numbers. Although the succession of thermophilic bacteria and thermophilic actinomycetes clearly reflected the effect of seeding, no clear difference was observed in the overall rate of composting or quality of the composted product.     

Occurrence of Aspergillus fumigatus during composting of sewage sludge.

Aspergillus fumigatus, a medically important fungal opportunist and respiratory allergen, was isolated from woodchips and sewage sludge used in the production of compost at the U.S. Department of Agriculture's composting research facility in Beltsville, Md. It was also regularly isolated as a dominant fungus during forced aeration composting and after 30 days in an unaerated stationary curing pile; in both cases, the fungus was found in pile zones with temperatures less than 60 degrees C. Compost stored outdoors in stationary unaerated piles from 1 to 4 months after screening out of woodchips contained easily detectable amounts of A. fumigatus in the exterior pile zones (0- to 25-cm depths). Semiquantitative studies of the airspora at the composting site revealed that A. fumigatus constituted 75% of the total viable mycoflora captured. At locations 320 m to 8 km from the compost site, the fungus constituted only 2% of the total viable mycoflora in the air. Of 21 samples of commercially available potting soil, one had levels of A. fumigatus nearly equivalent to those of 1-month-old storage compost; 15 others had lower but detectable levels.     

Effect of seeding during thermophilic composting of sewage sludge.

Serological analysis of the O and K antigens was performed on 324 isolates of Vibrio parahaemolyticus obtained from three hydrobiologically dissimilar aquatic environments. Only 50.9% of the strains could be serotyped. The largest number of untypable strains and the lowest serological diversity were observed from the freshwater collection. Three serotypes, O2:K28, O5:K17, and O2:K3, dominated among all biotopes. There appears to be some distinction between serotypes of environmental and clinical origins.     

Occurrence of Aspergillus fumigatus during composting of sewage sludge.

Aspergillus fumigatus, a medically important fungal opportunist and respiratory allergen, was isolated from woodchips and sewage sludge used in the production of compost at the U.S. Department of Agriculture's composting research facility in Beltsville, Md. It was also regularly isolated as a dominant fungus during forced aeration composting and after 30 days in an unaerated stationary curing pile; in both cases, the fungus was found in pile zones with temperatures less than 60 degrees C. Compost stored outdoors in stationary unaerated piles from 1 to 4 months after screening out of woodchips contained easily detectable amounts of A. fumigatus in the exterior pile zones (0- to 25-cm depths). Semiquantitative studies of the airspora at the composting site revealed that A. fumigatus constituted 75% of the total viable mycoflora captured. At locations 320 m to 8 km from the compost site, the fungus constituted only 2% of the total viable mycoflora in the air. Of 21 samples of commercially available potting soil, one had levels of A. fumigatus nearly equivalent to those of 1-month-old storage compost; 15 others had lower but detectable levels.     

Structural changes in lipid-free humic acids during composting of sewage sludge

Structural changes in humic acids (HAs), extracted after lipid removal from sewage sludge during composting, were investigated using various chemical methods (elemental analysis, Fourier transform infrared spectroscopy and ¹³C-nuclear magnetic resonance (NMR) spectroscopy). Compared to non-purified HAs, lipid-free HAs (LFHAs) exhibit higher C and N contents and high absorbance around 1652, 1540 and 1230 cm⁻¹, which indicates the intensity of the etherified aromatic structures and nitrogen-containing components. Less absorbance around 2920, 1600, 1414 and 1100 cm⁻¹ could be assigned to their low level of aliphatic compounds, mainly those with a carboxyl group. According to ¹³C-NMR spectroscopy, almost 45% of aliphatic structures are removed by lipid extraction and these correspond mainly to long-chain fatty acids. During composting, significant decomposition of non-substituted alkyl structures and N-containing components occurred, increasing the relative intensity of etherified aromatic structures.     

Evolution of organic matter from sewage sludge and garden trimming during composting

To use compost appropriately in agriculture it is extremely important to estimate the stabilization level of the organic matter. In this work, two different piles of compost were studied by means of (i) humification parameters (degree of humification--DH, humification rate--HR, humification index--HI) prior to and after enzymatic hydrolysis of the extracted organic carbon, (ii) water-soluble organic carbon (WSOC) and (iii) water-soluble nitrogen. A significant relationship between composting time, WSOC and humification parameters after enzymatic hydrolysis (DHenz; HRenz; HIenz) was found.     

Organic matter transformations and kinetics during sewage sludge composting in a two-stage system

The use of different proportions of rape straw and grass as amendments in the composting of dewatered sewage sludge from a municipal wastewater treatment plant was tested in a two-stage system (first stage, an aerated bioreactor and second stage, a periodically turned windrow). The composition of feedstock affected the temperature and organic matter degradation in the bioreactor and the formation of humic substances, especially humic acids (HA), during compost maturation in the windrow. The total HA content (the sum of labile and stable HA) increased according to first-order kinetics, whereas labile HA content was constant and did not exceed 12% of total HA. Δlog K of 1.0–1.1 indicated that HA was of R-type, indicating a low degree of humification. Temperature during composting was the main factor affecting polymerization of fulvic acids to HA and confirmed the value of the degree of polymerization, which increased only when thermophilic conditions were obtained.     

Relationships between biological and chemical parameters on the composting of a municipal solid waste

The aim of this work was to study the combined relationships between biological and chemical parameters with the humification index (HI) and degree of polymerisation (DP) during the composting of a municipal solid waste. During the composting, biological parameters increased during the first 15 days. After the second week, the dehydrogenase, urease, β-glucosidase, phosphatase and arylsulphatase activities decreased 64%, 50.1%, 49.6%, 24.1% and 58.3%, respectively, compared with their initial values, possibly due to the decreasing of the water-soluble carbon content (WSC). The WSC contents decreased possibly due to the degradation of the microorganisms as carbon and energy sources. The HI increased (66% compared to the initial values) indicating an increase in the structural complexity of the humic substances. The factorial analysis indicates a relationship between the biological properties, WSC and HI and DP. The linear regression analysis indicates the high correlation coefficients found between the HI and DP with chemical and biological properties, and therefore, it can be concluded that combination of chemical and biological parameters can be used to determine the compost maturity.     

Transformations of water soluble organic materials during thermophilic composting of sewage sludge

Sewage sludge was composted by adding wood chips as a bulking agent. The decomposition of the cellulosic material was ascertained by measuring the transient concentrations of water soluble sugars. The concentrations were found to increase in accordance with the decomposition of the cellulosic material, provided the operating temperature was kept at a level appropriate for the activity of microorganisms.Two kinds of concentrations of water soluble sugars were measured. One was on the concentration of the total sugars determined by the calorimetric method of Dubois. The other was on the concentration of the reducing sugars determined by the Somogyi-Nelson method. The pattern of HPLC (High Pressure Liquid Chromatogram) was determined utilizing a wave length of 280 nm. Time courses of the sugars concentrations and the HPLC pattern enabled us to detect two sources of cellulosic materials: one from the sewage sludge and the other from the wood chips. The former appears to be decomposed by thermophilic bacteria and thermophilic actinomycetes, whereas the latter is decomposed by thermophilic fungi.     

Comparative analysis of Cryptosporidium, Giardia and indicator bacteria during sewage sludge hygienization in various composting processes

AIMS: To evaluate the suitability of Clostridium perfringens, Escherichia coli and enterococci as indicator organisms for Cryptosporidium and Giardia in treated sludge. METHODS AND RESULTS: Occurrence of Cryptosporidium oocysts and Giardia cysts, detected and enumerated by direct immunofluorescence microscopy, were compared with counts of indicator bacteria during six different sewage sludge hygienization processes, including closed reactor and open windrow composting, and sludge sanitation by quicklime or peat addition. No statistical correlation existed between the counts of indicator bacteria, Cl. perfringens, E. coli, and enterococci and occurrence of Cryptosporidium or Giardia. In sludge end-products, Giardia cysts were detected more frequently than Cryptosporidium oocysts. SIGNIFICANCE OF THE STUDY: Direct analysis is the best method to confirm the presence of (oo)cysts in sludge.     

城市污水灌溉对植物栽培基质理化性质的影响

采用污水浇灌的方式,对尾叶桉、马占相思、小叶榕、阴香和美人蕉5种植物在塑料大棚内进行盆栽试验,研究了城市污水浇灌对植物栽培基质理化性质的影响.研究结果表明:随着浇灌污水浓度增加,植物栽培基质的容重降低,孔隙度增大,pH值有所降低,有机质含量有一定增加:全N含量降低,除阴香外,其余4种植物栽培基质的速效K、速效P含量增加.表明污水灌溉植物,增强了栽培基质的肥力,且栽培基质的全N、速效K、速效P含量有较大变化.     

Influence of humic substances on bioavailability of Cu and Zn during sewage sludge composting

Influence of humic substances (HS) on bioavailability of Cu and Zn was characterized during 120 days co-composting of sewage sludge and maize straw. At the initial stage of composting, Cu and Zn in sewage sludge were released as organic matter was degraded, and water soluble Cu and Zn increased markedly. Water soluble Cu and FA content decreased after 21 days whereas water soluble Zn increased during the whole process. Both HA-Cu and HA-Zn were significantly and positively correlated with HA and H/F, respectively. At the end of composting, the distribution coefficients of HA-Cu and HA-Zn reached 27.50% and 3.33% respectively with HA-Cu/HA-Zn ratio increased from 1.29 to 2.73. The results suggest that Cu combined with HA more strongly than Zn, and composting treatment could decrease bioavailability of Cu markedly.     

Humic substances change during the co-composting process of municipal solid wastes and sewage sludge

The change of the degree of stability of compost during the composting process was a kind of guideline for our study. This stability was estimated by monitoring the chemical fractionation (extraction of humic and fulvic acids, and humin) during two cycles of composting. Change of humin (H), humic-like acid carbon (CHA) and fulvic-like acid carbon (CFA) fractions during the composting process of municipal solid wastes were investigated using two windrows W1 (100% of municipal solid wastes) and W2 (60% of municipal solid wastes and 40% of dried sewage sludge). Humin and fulvic acid fractions in the two windrows decreased since the start of composting process and tend to stabilize. At the end of composting process, humic acid fraction is more important in the windrow without sludge (W1) than the one with sludge (W2). The humification indexes used in this study showed that the humic-like acid carbon fraction production takes place largely during the phase of temperature increase (thermophilic phase), and it appeared very active in the windrow W2. At the end of composting process, the E₄/E₆ ratio value indicated that the compost of W1 is more mature than the compost of W2. The humification ratio (HR) allowed a correct estimation of compost organic matter stabilization level.     

Decrease of enteric micro-organisms from rural sewage sludge during their composting in straw mixture

AIMS: To study the decrease of enteric micro-organisms including viable nematode eggs, enteroviruses, faecal indicators (Escherichia coli and enterococci) and pathogenic bacteria (Listeria monocytogenes, Salmonella sp. and Clostridium perfringens) of a rural sewage sludge when it is composted for 7 months in mixture with straw. METHODS AND RESULTS: Numbers of the test organisms and the physico-chemical parameters were measured on a monthly basis on the mixture, on the compost after being turned, and on the pile in three positions representing the part by which air is incoming, the bottom of the pile and the part through which air is outgoing. The lowest temperature in the pile was observed at the bottom, where it did not exceed 50 degrees C against 66 degrees C in the two other areas. There were no significant differences between the three areas in terms of micro-organism survival. Infectious enteroviruses were inactivated rapidly and were not found after the first turning whereas some genomes were detected until after the third turning. Escherichia coli and enterococci presented a similar survival rate and their number decreased by 4 log(10) whereas Salmonella decayed at a greater rate than L. monocytogenes. The numbers of C. perfringens decreased gradually to reach a final concentration in the mature compost of about 10(2) CFU g(-1) dry matter (d.m.), which was similar to that of the faecal indicators. CONCLUSIONS: The hygienic effect of sludge composting in mixture with straw results in a significant reduction of enteric micro-organisms, the concentration of the faecal indicators in the final product being < 64 most probable number g(-1) d.m. The concentrations of Salmonella, enteroviruses and viable nematode eggs in the final product were not detectable which is in accordance with the French legislation. SIGNIFICANCE AND IMPACT OF THE STUDY: The results which pointed out the different behaviour of the test micro-organisms reflect the difficulty to propose a relevant indicator of hygienization. Otherwise, they show that composting is an efficient means for hygienization of sludge of rural wastewater treatment, where the straw is available close to their place of production.     

Monitoring of microbial populations and their cellulolytic activities during the composting of municipal solid wastes

Seasonal changes in microbial populations and the activities of cellulolytic enzymes were investigated during the composting of municipal solid wastes at Damietta compost plant, Egypt. The changes in temperature, pH and carbon/nitrogen (C/N) ratio were also monitored. The results obtained showed that the temperatures of the windrows in all seasons reached the maximum after 3 weeks of composting and then decreased by the end of the composting period (35 days), but did not reach ambient temperature. Marked changes in pH values of the composts in all seasons were found, but generally, the pH was near neutrality. Significant increases in the size of the microbial populations were obtained in autumn and spring seasons compared to summer and winter seasons. The activities of cellulases were also higher in the autumn and spring seasons than in the summer and winter seasons. The decrease in C/N ratio in autumn and spring was higher than in summer and winter. It was evident that the degradation of organic matter increased by an increase in the microflora and its cellulolytic activities.