Organic Waste Samples Research Articles

Application of XGBoost for Fast Identification of Typical Industrial Organic Waste Samples with Near-Infrared Hyperspectral Imaging

Waste material identification is an essential part of waste recycling and treatment. Hyperspectral imaging (HSI) enables fast, accurate, nondestructive, and non-invasive identification of waste materials. In this study, HSI-based classification of typical industrial organic waste that cannot be sorted via traditional methods has been explored, namely, leather, paper, plastic, rubber, textile, and wood. The extreme gradient boosting (XGBoost) algorithm, a supervised machine learning algorithm that has never been investigated for waste identification-related fields, was adopted. The results show that XGBoost obtained a higher pixel-wise weighted average F1-score of 82.72% and a faster prediction time of 270 ms for the tested images compared with the commonly used partial least squares-discriminant analysis (77.83% and 444 ms). XGBoost was more effective and efficient in aiding HSI identification and classification of industrial organic waste. The technique can be a significant advancement in the development of an online sorting or identification platform, affording significant labor cost reduction, time savings, and the provision of a stable, accurate, and rapid method for waste intelligent identification.

Assessing Physiochemical Characteristics of Agricultural Waste and Ready Compost at Wadi Al-Far'a Watershed of Palestine.

The Wadi Al-Far'a Watershed (WFW) is one of the most important agricultural lands in Palestine where considerable amounts of organic wastes are generated. Yet, mismanagement of agricultural waste, including random disposal and/or burning, is a prevalent practice in the WFW. Such a practice might result in greenhouse gas emissions and leachate penetration into underlying soil and groundwater. To encourage compost production in the WFW as an efficient way for organic agricultural waste treatment and emission reduction, this study aims at evaluating the quality of both raw organic agricultural waste and ready compost, locally produced or imported. The evaluation considers the physiochemical characteristics as well as the heavy metal contents. The analysis of 17 samples of raw organic agricultural waste showed a good potential for compost production due to the high content of organic matter and other nutrients such as nitrogen and phosphorus. The analysis of 15 ready compost samples, however, showed that compost quality is relatively low due to the high electrical conductivity and low moisture content measurements as well as the high levels of sodium, chloride, and potassium. Furthermore, heavy metal contents of both raw organic agricultural waste and ready compost samples are less than the limits specified by the Palestinian and international standards. Therefore, local farmers can safely use raw organic agricultural waste generated in the WFW for compost production. Composting will not only enhance soil reclamation and crop production but also protect human health and the environment and promote sustainable economic development.

Studies on Degradation of Organic Food Waste, Municipal Solid Waste, and Agriculture Waste from Kolhapur, Maharashtra, India

Present study deals with different types of organic waste samples collected from different areas of Kolhapur city such as food waste, agricultural waste and municipal waste. Different organic waste samples were degraded with increase in retention time from 1 to 50 days. The parameters like pH, EC, Nitrogen, Phosphorous and Potassium were studied after every 10 days of interval. The results were interesting showing increased degradation activity by using microorganisms. It is also evident in the study that if less energy is available for growth of microorganism less microbial biomass is produced. The result suggests that food waste degradation shows decrease in nitrogen, potassium, and phosphorous whereas organic carbon, organic matter was also decreased. Agriculture waste degradation shows organic carbon, organic matter, nitrogen decrease and increase in phosphorus, potassium. Municipal solid waste degradation shows decrease in nitrogen, phosphorus and slight increase in potassium and decrease in organic carbon and organic matter

Isolation and Characterization of Polyhydroxybutyrate (PHB) Producing Microorganisms from Karad Region, Maharashtra

World population is increasing day by day and to satisfy their various needs, plastic material become part and parcel of life. Millions of tons of these non degradable plastics accumulate in the environment per year and cause hazardous effects on flora and fauna. Hence there was ever pending search for bioproduct which can substitute this nonbiodegradable plastic. Polyhydroxybutyrates (PHB) are drawing much attention as they are biodegradable, environmentally friendly, and also biocompatible bioplastics. In the present study an attempt was made to isolate and characterize the PHB producing microorganisms from Karad region of Maharashtra. Total 75 isolates obtained from soil, spent wash, pond water, dairy effluent, cow dung, soil and organic waste samples were enriched using mineral salt medium and then screened primarily for PHB producers by Sudan Black B plate staining method followed by secondary screening using Nile blue plate assay method. As a result of screening, 11 PHB producing potential isolates were obtained which were then studied for morphological, biochemical and enzymatic characters. By referring Bergeys Manual of Determinative Bacteriology and 16 S r RNA technique these 11 PHB producing isolates were identified and found from genera Bacillus, Candida, Citrobacter and Klebsiella, Staphylococcus and Rhodococcus.

Protatif anaerobik biyoreaktör tasarımı ve üretim denemeleri

Biogas is a flammable gas mixture that can be produced by anaerobic digestion of organic wastes. It contains 50-65% methane gas, 35-50% carbon dioxide (CO2) gas and 100-1000 ppm hydrogen sulfide (H2S) gas in biogas. One of the biggest disadvantages in biogas production technologies is the cost of purification technologies that convert biogas to biomethane. In this study, a portable, intermittent anaerobic bioreactor and a 20 liter gasometer were designed. The purpose of using gasometer is to ensure the adsorption of H2S and CO2 gases in the raw biogas coming out of the bioreactor, using only the production power of the biogas without requiring any external intervention. In this context, only the produced biogas amount and biogas content of the batch bioreactor with an effective volume of 5 liters were tested twice. Within the scope of this production, a sample was taken every five days from the start of gas production in the batch reactor and the removal of chemical oxygen demand was compared with the initial situation. Each production trial lasted 36 days. Then, the second stage of the study was started and the biogas outlet was directly connected to the gasometer tank. At this stage, biogas and organic waste samples were taken from the gasometer and batch reactor every five days and tested. While the H2S and CO2 contents of the biogas formed as a result of the experiments without gasometer were 558 ± 55 ppm and 55.4 ± 2.9%, respectively, these values were found to be 45 ppm and 24.5%, respectively, as a result of the production with gasometer. As a result, it has been determined that an industrial-scale gasometer system adsorbs approximately 88% of H2S and 55% of CO2 in biogas without requiring an extra biogas purification unit. For further studies, changing the gasometer volume and increasing the holding times of the water in the gasometer are recommended as CO2 and H2S concentrations can be further reduced.

Improved xylitol production by the novel inhibitor-tolerant yeast Candida tropicalis K2

ABSTRACT Production of potential value-added products from different lignocellulosic biomass is becoming more common due to the availability of the feedstocks in abundance and the environment- friendly nature of the microbial production process. Due to the large array of its applications in the pharmaceutical and food sectors, xylitol is considered as potential value-added compound for production. In this study, organic waste samples were collected from various habitats and screened for potential yeast isolates for xylitol production. Among 124 tested isolates, Candida tropicalis K2 showed the highest potential for xylitol production as well as inhibitors tolerance (Furfural, 5-hydroxymethyl furfural and acetic acid) phenotypes. C. tropicalis K2 produced 90 g/L of xylitol in batch fermentation (100 g/L xylose supplemented with 20 g/L of glycerol as co-substrate) with the yield and productivity of 0.90 g/g and 1.5 g/L.h, respectively, at pH 5.5 and 30°C temperature. Together, >10% higher xylitol yield was achieved when glycerol was used as a co-substrate with pure xylose. Moreover, with non-detoxified corncob and Albizia pod hydrolysates, C. tropicalis K2 isolate produced 0.62 and 0.69 g/g of xylitol yields and 1.04 and 0.75 g/L.h xylitol productivities, respectively. Thus, C. tropicalis K2 isolate could be considered as promising candidate for xylitol production from different lignocellulosic biomass. HIGHLIGHTS Candia tropicalis K2 isolate was screened from natural sites of biomass degradation and characterized for xylitol production. Non-detoxified Albizia pod and corncob hydrolysates were explored for xylitol production using selected C. tropicalis K2 isolate. A maximum of 0.90 g/g yield and 1.07 g/L.h xylitol productivity was achieved with pure xylose. A >10% increase in xylitol yield was achieved using glycerol as a co-substrate.

Prediction of biochemical methane potential of urban organic waste using Fourier transform mid-infrared photoacoustic spectroscopy and multivariate analysis

Biochemical methane potential (BMP) assays are widely used to assess feedsocks in oder to control the process of biogas production. However, the continuous evaluation of feedstocks using a BMP assay is expensive, time-consuming and challenging. In this study, Fourier transform mid-infrared photoacoustic spectroscopy (FTIR-PAS) was used to predict the BMP values of 87 urban organic waste (UOW) samples derived from different sources in Denmark. The developed model of BMP prediction showed a coefficient of determination (R2) of 0.86 and a root mean square error (RMSE) of 59.3 mL CH4/g VS in prediction. The interpretation of the regression coefficients used in the calibration showed a positive correlation with BMP for relatively easily degradable compounds, such as aliphatics, most likely lipids and amides most likely in proteins, while a negative correlation was found with lignin and hemicellulose.

Feeding strategies for small-scale rearing black soldier fly larvae (Hermetia illucens) as organic waste recycler

Processing organic waste using black soldier fly (BSF)-based technology offers a promising alternative for sustainable organic waste management and urban sanitation. This study was conducted to assess the influence of feeding strategies on the efficacy of BSF larvae to recycle organic wastes into value products. Fruit waste and chicken manure were used as organic waste samples while commercial chicken feed was used as a control, and were processed for 15 days in circular plastic containers (Ø 30 × 12 cm) with 50; 100; 150; and 200 mg/larva/day continuous and batch feeding diets, using 500 four-day-old larvae per diet, repeated four times. Larval survival rates were not significantly affected by the feeding strategies. However, average larval biomass of 83.69 ± 13.04 g and 82.46 ± 08.52 g was achieved for the continuous and batch feeding strategies, respectively, under favorable conditions. Larval feed reduction rates ranged from 24.65 ± 03.48% to 72.78 ± 01.48% and 24.52 ± 0.27% to 72.25 ± 12.13% with continuous and batch feeding strategies, respectively, and were significantly affected by the different daily diets. On the other hand, the bioconversion rates ranged from 13.34 ± 0.26% to 50.82 ± 02.27%, and the highest values were observed with the continuous feeding diets. This study confirms the efficacy of BSF larvae to thrive in different organic substrates and shows that the continuous feeding strategy can be better and enhance a sustainable small-scale organic waste management.

Presentation of Three Novel Tailed Phages Targeting Multiple Strains of Pseudomonas syringae.

Background: Pseudomonas syringae are ubiquitous epiphytic plant pathogens infecting a wide range of important agricultural plant species. Bacteriophages has been proposed as biocontrol agents against plant pathogens, however, in order to utilize this approach, a deeper understanding of phage diversity and phage-host interactions is required. Materials and Methods: Phages targeting P. syringae GAW0113 were isolated from organic waste samples. Three distinct phage isolates were purified and subjected to whole-genome sequencing, comparative genomics, transmission electron microscopy and host-range assay using a wide selection of diverse P. syringae isolates. Results: The three phage isolates, Pseudomonas phage Bertil, Misse, and Strit, were shown to have podovirus morphology with a short tail stub and isometric head. They had double-stranded DNA ranging from 41,342 to 41,374 bp in size comprising 50-51 open reading frames. The three phage genomes were highly similar and genomic comparison analyses showed that they all belong to the Autographiviridae family of the order Caudovirales. All three phages were shown to have a narrow host-range. Conclusions: The three phages were shown to share morphological and genomic features with other phages in the Autographiviridae family, however, based on the limited nucleotide similarity we propose that the phages constitute a novel genus. All three phages were found to infect multiple strains of P. syringae covering several phylogroups.

Isolation and characterisation of novel phages infecting Lactobacillus plantarum and proposal of a new genus, \u201cSilenusvirus\u201d

Bacteria of Lactobacillus sp. are very useful to humans. However, the biology and genomic diversity of their (bacterio)phage enemies remains understudied. Knowledge on Lactobacillus phage diversity should broaden to develop efficient phage control strategies. To this end, organic waste samples were screened for phages against two wine-related Lactobacillus plantarum strains. Isolates were shotgun sequenced and compared against the phage database and each other by phylogenetics and comparative genomics. The new isolates had only three distant relatives from the database, but displayed a high overall degree of genomic similarity amongst them. The latter allowed for the use of one isolate as a representative to conduct transmission electron microscopy and structural protein sequencing, and to study phage adsorption and growth kinetics. The microscopy and proteomics tests confirmed the observed diversity of the new isolates and supported their classification to the family Siphoviridae and the proposal of the new phage genus “Silenusvirus”.

Analyzing the stability level of organic waste by the static respiration index and dynamic respiration index

Stability is a parameter that reveals the extent of decomposition of biodegradable organic matter. Various methods are employed to measure the stability level of organic materials, including the static respiration index (SRI) and dynamic respiration index (DRI). In this study, the characteristics and stability of food waste, garden waste, municipal organic waste, fruit waste, tofu factory waste, and cow dung samples used in the study were identified and analyzed on the basis of the water content, volatile solids, C/N ratio, lignin content, and SRI and DRI values. In addition, an appropriate method for the further processing of unstable organic waste samples was determined. Organic waste samples were collected from nine places. Results revealed that the tofu factory waste samples exhibit the highest SRI and DRI values of 13.3995 mgO2g−1OM−1h−1 and 148.3747 mgO2g−1OM−1h−1 respectively. The composting results for tofu factory waste samples and cow dung with coconut shells as the bulking agent for 14 days revealed that the highest percentage of SRI decrease for tofu factory waste was 99.94% on the 3rd day of composting. On the other hand, the highest percentage of SRI decrease for the cow dung samples is 99.17% on the 7th day of composting.

Organic Fraction of Municipal Solid Waste (OFMSW) Using Continuous-Flow Anaerobic Reactor

This manuscript describes the particle size distribution based model.This model accounts for the degradation and methane production from the anaerobic digestion of the (OFMSW) organic fraction of municipal solid waste. The model also shows the reduction in cost of solid waste treatment. Analysis was done based on laboratory test, carried out to test the operating parameter such as Ammonia, PH, Temperature, volume of gas, total solid, volatile solid, nitrate, nitrite, phosphate and conductivity while Volatile fatty acid was negligible. The organic waste samples used was cow dung, and was digested using a continuous flow stirred reactor, which was constructed locally at the institution hydraulic laboratory. Results from the test and analysis reveals high concentration of ammonia which inhibited the production of gas. The total solid content was observed to determine the rate of organic loading of the reactor. The biogas production from the continuous flow reactor, contains ammonia concentration of 460mg/l ,385mg/l, 300mg/l, 193mg/l, 120mg/l and 130mg/l, under similar operating PH of 6.68. There was no contribution of biogas production from inoculation. Total volume of biogas produced was calculated and was found to be 0.036m3, 0.040m3, 0.055m3 0.053m3and varied according to PH range of 6.67 to 7.2. The result also shows that at a PH of 7.2, ammonia concentration was high, limiting the methane production rate. The highest form or concentration of nitrate and nitrite occurs at the end of the detention period. Decrease in the PH value and conductivity was a strong indication of the present of nitrate and nitrite in the solution of the waste sample.

Siloxane compounds in biogas from manure and mixed organic waste: Method development and speciation analysis with GC-ICP-MS

A novel method for the determination of linear and cyclic siloxane compounds (L2, L3, D3, D4, D5, and D6) in biogas was developed by combining gas chromatography (GC) with inductively coupled plasma mass spectrometry (ICP-MS). Using a continuous liquid quench sampling system, biogas samples were collected from a Swiss biogas production plant processing manure and mixed organic wastes. Although significant concentrations of siloxanes are normally linked to biogas from wastewater treatment plants (WWTP) or landfill gas, manure and mixed organic waste samples also showed values in the range of 0.1 mgSi Nm−3, which would be particularly critical for appliances such as solid oxide fuel cells (SOFC). The GC-ICP-MS method showed very good linearity for all the investigated compounds (R2 between 0.999 and 1.000). The limits of detection and quantification (LOD and LOQ) in the gas for cyclic compounds, such as D5, vary based upon the used sampling conditions (approximate range of 0.002–0.004 mgSi Nm−3 and 0.007–0.014 mgSi Nm−3, respectively). To the best of our knowledge, these LOD and LOQ values are by far among the lowest reported in literature and they satisfy the EURAMET (the European Association of National Metrology Institutes) requirements, which fix recommended levels for Si total amounts between 0.1 and 0.3 mgSi Nm−3 for measurement in biogas or bio-methane. The GC-ICP-MS method was evaluated by comparing its performances with a flame ionization detector (FID), operated in parallel with ICP-MS, and with GC-MS (gas chromatography - mass spectrometry). The GC-FID showed higher detection limits and matrix effects than GC-ICP-MS. Nevertheless, it can still be suitable for an initial estimation of the siloxane compounds present in the biogas, at least for samples having relatively high concentration, by following some data treatment optimization. The GC-MS analyses were considered here as a further confirmation of the accuracy of the GC-ICP-MS results.

Conversion of organic biomedical waste into potential fertilizer using isolated organisms from cow dung for a cleaner environment.

Management of organic biomedical waste is a global quandary, and it is becoming difficult to confront day by day. Conversion of organic biomedical waste into fertilizer is of great concern. In the present research, organic biomedical waste samples (blood swabs, dressing swabs, and used cotton) were collected then after cow dung was collected in sterile container and immediately transported to the laboratory and screened for any gastrointestinal infection by using routine microscopy for intestinal parasitic infection, routine bacterial culture, and fecal occult blood for any intestinal bleeding. Then after, the pure culture of organisms and fungus were prepared, and further samples were subjected to degradation for 288 h by using various organisms and fungus. Then after, the specific quantity of biomedical waste was subjected for incineration. The physicochemical parameters of biomedical waste samples were analyzed. Then treated samples were mixed with soil to confirm a role as potential fertilizer. Then after, tomato plantation was done and phytochemical parameters of tomato plant were analyzed. This study states that organic biomedical waste produces a sanitary and stable fertilizer.

Generation of Electricity Using Microbial Fuel Cell (MFC) from Sludge

Microbial fuel cell (MFC), recently, is considered as a promising alternative to traditional power sources as it can use microorganisms to transform chemical energy of organic compounds into electricity. In future, microbial production of electricity may become an important form of bioenergy because electricity extraction is possible through MFC using wide range soluble or nonsoluble complex organic wastes as a renewable biomass. In this study, single chamber MFC and double chambers MFCs were used to production and enrichment a microbial consortium for electricity generation from organic waste samples. Potential electrogenic bacteria were also isolated from anode, analyzed and evaluated. Most of them were Gram negative and fermentative organisms. Their electrogenic role was promising generating upto 5.05 volts and 4.72 mA when combined five) double chambers in series connection. Isolation of these bacteria and employing these for generation of electricity may bring potential power sector endeavor in future.
 Bangladesh J Microbiol, Volume 35 Number 1 June 2018, pp 23-26

Conversion of organic biomedical waste into value added product using green approach.

Sustainable organic biomedical waste management is a difficult challenge as this has become one of the serious hazardous wastes. Improper disposal of organic biomedical waste can lead to direct and indirect transmission of diseases. In the present research, the organic biomedical waste samples (32g blood swabs, 12g dressing swabs, and 6g used cotton) were treated with Azadirachta indica ("Neem") and Nicotiana tabacum ("Tobacco") extracts at various concentrations and kept for 96-h degradation, followed by evaluation of physicochemical parameters. The physicochemical results of organic biomedical waste like pH of the experimental sets were within the optimum range and there was 63.33% of decrease of TDS, 86.15% and 95.30% reduction of BOD and COD, respectively was observed at the end of 96h. The residues were mixed with 1000g soil to confirm their role as a potential fertilizer. The physicochemical parameters of soil sample F6 (neem+tobacco) show an excellent result among all. The phytochemical parameters of a plant were also enhanced as compared to control. The soil samples and the tomato plants were also not polluted by the heavy metals, they are within the limit given by WHO. The present study deals with the conversion of organic biomedical waste into potential fertilizer by using plant extracts which can purely be financially profitable to the farmer.

Evaluation of Biogas Production from the Co-Digestion of Municipal Food Waste and Wastewater Sludge at Refugee Camps Using an Automated Methane Potential Test System

The potential benefits of the application of a circular economy—converting biomass at Za’atari Syrian refugee camps into energy—was investigated in this study. Representative organic waste and sludge samples were collected from the camp, mixed in different ratios, and analyzed in triplicate for potential biogas yield. Numerous calorific tests were also carried out. The tangential benefit of the co-digestion that was noticed was that it lowered the value of the total solid content in the mixture to the recommended values for wet digestion without the need for freshwater. To test the potential methane production, the automated methane potential test system (AMPTS) and the graduated tubes in the temperature-controlled climate room GB21 were utilized. Also, calorific values were determined for the organic waste and sludge on both a dry and a wet basis. The maximum biogas production from 100% organic waste and 100% sludge using AMPTS was 153 m3 ton−1 and 5.6 m3 ton−1, respectively. Methane yield reached its maximum at a Vs sub/Vs inoculum range of 0.25–0.3. In contrast, the methane yield decreased when the Vs sub/Vs inoculum exceeded 0.46. The optimum ratio of mixing of municipal food waste to sludge must be carefully selected to satisfy the demands of an energy production pilot plant and avoid the environmental issues associated with the sludge amount at wastewater treatment plants (WWTPs). A possible ratio to start with is 60–80% organic waste, which can produce 21–65 m3· biogas ton−1 fresh matter (FM). The co-digestion of organic waste and sludge can generate 38 Nm3/day of methane, which, in theory, can generate about 4 MW in remote refugee camps.

Biogas Production from Dining Hall Waste and Landfill Leachate in a Two Stage R&D Facility

Taking into consideration recovery dining hall waste from university cafeteria and nutrient reduction of landfill leachate, they were mixed at a temperature of 36±1°C and for a period of 90 days in a two stage biogas production R&D facility with a total volume of 5m3, and then experiments were done. Experiment-I was performed to engage the second digester as a priority, and Experiment-II was performed to engage the first digester. After the required bacteria formation was ensured, the first digester was daily fed with mixture of dining hall waste with 10% solid matter content and landfill leachate weighing 167 kg in total regularly feeding in Experiment-III. Analyses and measurements of total solids (TS), total volatile solids (TVS), C% and N% percentages, pH, volatile fatty acid (VFA) and inhibitive of the organic waste samples were measured from the feedstock, digesters, and fertilizer tanks. In addition, daily biogas samples were taken and concentrations of CH4(%) with mass flow rate of the biogas were measured. The results showed that in case dining hall waste and landfill leachate was mixed, the first digester worked at pH values of around 4.5–5.5 and performed the task of hydrolysis and acidification. The second digester performed the task of bio-methanation successfully.

Biodegradability of Formulated Enzymatic Solution: An Alternative Waste Reduction System

Solid waste and air pollution are never ending environmental problems that can be partially solved by turning waste into useful bio-products. In this study, enzymatic solutions were developed by formulating enzymatic solutions from fish intestines and fruit peels. This aimed to help in biodegradation of organic solid wastes. Organic waste samples were treated with formulated enzymatic solutions for 7 days in aerated set-up for aerobic degradation. Biodegradability and odor of the waste samples were compared with commercial enzymatic solution. Determination of evolved carbon dioxide (CO2) using gravimetric analysis (GA) was used to determine the percent biodegradability, Dt, of organic solid waste and odor-ranking method was used to determine the odor intensity of the organic waste samples. The result showed that the weight loss and percentage biodegradability of organic waste sample treated with formulated enzymatic solution is comparable with that of the commercial enzymatic solution. In terms of odor intensity, waste treated with the product, formulated enzymatic solution (FES) is also comparable to the waste treated with commercial enzymatic solution. Thus, implying that the developed FES is as efficient as that of the commercial enzymatic solution. These significant results will be helpful to future researchers in providing ways on improving the degradation of organic solid waste and mitigating the increasing glitches on our environment. Enzyme kinetics, physical and chemical properties studies of the solution were recommended for future researchers to accurately determine the effectiveness of the formulated enzymatic solution in the degradation of organic solid waste.

Fast determination of trace elements in organic fertilizers using a cup-horn reactor for ultrasound-assisted extraction and fast sequential flame atomic absorption spectrometry

A fast and accurate method based on ultrasound-assisted extraction in a cup-horn sonoreactor was developed to determine the total content of Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn in organic fertilizers by fast sequential flame atomic absorption spectrometry (FS FAAS). Multivariate optimization was used to establish the optimal conditions for the extraction procedure. An aliquot containing approximately 120 mg of the sample was added to a 500 µL volume of an acid mixture (HNO3/HCl/HF, 5:3:3, v/v/v). After a few minutes, 500 µL of deionized water was added and eight samples were simultaneously sonicated for 10 min at 50% amplitude, allowing a sample throughput of 32 extractions per hour. The performance of the method was evaluated with a certified reference material of sewage sludge (CRM 029). The precision, expressed as the relative standard deviation, ranged from 0.58% to 5.6%. The recoveries of analytes were found to 100%, 109%, 96%, 92%, 101%, 104% and 102% for Cd, Cr, Cu, Mn, Ni, Pb and Zn, respectively. The linearity, limit of detection and limit of quantification were calculated and the values obtained were adequate for the quality control of organic fertilizers. The method was applied to the analysis of several commercial organic fertilizers and organic wastes used as fertilizers, and the results were compared with those obtained using the microwave digestion procedure. A good agreement was found between the results obtained by microwave and ultrasound procedures with recoveries ranging from 80.4% to 117%. Two organic waste samples were not in accordance with the Brazilian legislation regarding the acceptable levels of contaminants.