Composition and production rate of medical waste from a small producer in Greece

The objective of this work was to determine the composition and production rate of medical waste from the health care facility of social insurance institute, a small waste producer in Xanthi, Greece. Specifically, produced medical waste from the clinical pathology (medical microbiology) laboratory, the X-ray laboratory and the surgery and injection therapy departments of the health facility was monitored for six working weeks. A total of 240 kg medical solid waste was manually separated and weighed and 330 L of liquid medical waste was measured and classified. The hazardous waste fraction (%w/w) of the medical solid waste was 91.6% for the clinical pathology laboratory, 12.9% for the X-ray laboratory, 24.2% for the surgery departments and 17.6% for the injection therapy department. The infectious waste fraction (%w/w) of the hazardous medical solid waste was 75.6% for the clinical pathology laboratory, 0% for the X-ray laboratory, 100% for the surgery departments and 75.6% for the injection therapy department. The total hazardous medical solid waste production rate was 64 ± 15 g/patient/d for the clinical pathology laboratory, 7.2 ± 1.6 g/patient/d for the X-ray laboratory, 8.3 ± 5.1 g/patient/d for the surgery departments and 24 ± 9 g/patient/d for the injection therapy department. Liquid waste was produced by the clinical pathology laboratory (infectious-and-toxic) and the X-ray laboratory (toxic). The production rate for the clinical pathology laboratory was 0.03 ± 0.003 L/patient/d and for the X-ray laboratory was 0.06 ± 0.006 L/patient/d. Due to the small amount produced, it was suggested that the most suitable management scheme would be to transport the hazardous medical waste, after source-separation, to the Prefectural Hospital of Xanthi to be treated with the hospital waste. Assuming this data is representative of other small medical facilities, medical waste production can be estimated for such facilities distributed around Greece.     

Large scale study on measurement of respiration activity (AT(4)) by Sapromat and OxiTop

In the run-up for amending the Austrian landfill ordinance, parameters were developed to assess the stability/reactivity of mechanically–biologically pretreated residual wastes. The Landfill Ordinance 2008 regulates limit values for Respiration Activity (=“Atmungsaktivität”) RA₄ (AT₄) < 7 mgO₂ * (g dry matter (DM))^?1, Gas Generation Sum GS₂₁ < 20 Nl * kg DM^?1 and alternatively Gas Evolution (=“Gasbildung”) GB₂₁ < 20 Nl * kg DM^?1. Methods for analysing these parameters were established by the Austrian Standards Institute (2004). As laboratory practice shows, these methods also are used for the assessment of other wastes (sewage sludge, commercial waste, material from abandoned sites, biowaste compost). For measurement of respiration activity in Austria mainly two methods are used: the Sapromat®-method and the OxiTop®-method. Whether respectively to what extent these two methods give same results, is discussed in this paper.Since 2009 at ABF-BOKU 169 respiration activity tests of samples taken from different stages of MBT – as well as biowaste composting processes, materials from landfills as well as abandoned sites and residues from anaerobic treatment plants were analysed parallel by Sapromat® and OxiTop®. The results manifest very strong correlation between the Sapromat® and OxiTop® method. The correlation coefficient is 0.993. As a very clear tendency OxiTop® gives lower amounts than Sapromat®. In average the lower values of OxiTop® are around 88%.     

Fossil and biogenic CO₂ from waste incineration based on a yearlong radiocarbon study

We describe the first long-term implementation of the radiocarbon (¹⁴C) method to study the share of biogenic (%Bio C) and fossil (%Fos C) carbon in combustion CO₂. At five Swiss incinerators, a total of 24 three-week measurement campaigns were performed over 1 year. Temporally averaged bag samples were analyzed for ¹⁴CO₂ by accelerator mass spectrometry. Significant differences between the plants in the share of fossil CO₂ were observed, with annual mean values from 43.4 ± 3.9% to 54.5 ± 3.1%. Variations can be explained by the waste composition of the respective plant. Based on our dataset, an average value of 48 ± 4%Fos C was determined for waste incineration in Switzerland. No clear annual trend in %Fos C was observed for four of the monitored incinerators, while one incinerator showed considerable variations, which are likely due to the separation and temporary storage of bulky goods.     

Municipal solid waste characteristics and management in Gümüşhane, Turkey

This paper presents a general overview of the current municipal solid waste (MSW) management in Gümüşhane Province, Turkey. In order to characterize the solid waste stream in the Municipality of Gümüşhane, a long-term study was conducted over a 52-week period between the spring of 2004 and the winter of 2005. In this study, percentage of components and specific weight of the MSW, the composting parameters (moisture content, total organic carbon, total nitrogen and pH), organic matter content, calorific value and the heavy metal concentrations (Cd, Cr, Cu, Ni, Pb, Zn, Fe, Mn, Co) of the compostable wastes sorted from the mixed MSW were determined and evaluated. In Gümüşhane, a mean of 70 tons of MSW are generated each day or 1 kg/day/capita. Approximately 4500 kg of the MSW were collected and sorted in a year, and the mean specific weight of these is 308 kg/m³. Approximately 30% of the MSW generated is compostable wastes and the yearly mean moisture content, organic matter content, C/N ratio and pH of these are 78%, 92.1%, 21.6/1 and 4.73, respectively, and approximately 24% of the MSW consists of recyclable materials. The recommended system deals with maximizing recycling and minimizing landfilling of the MSW, and consists of separation at source, collection, sorting, recycling, composting and sanitary landfilling. Heavy metal concentrations of the compostable wastes from the open dump were determined to decrease in the following order: Fe > Mn > Zn > Cr > Cu > Pb > Ni > Cd > Co.     

GHG emission factors developed for the recycling and composting of municipal waste in South African municipalities

GHG (greenhouse gas) emission factors for waste management are increasingly used, but such factors are very scarce for developing countries. This paper shows how such factors have been developed for the recycling of glass, metals (Al and Fe), plastics and paper from municipal solid waste, as well as for the composting of garden refuse in South Africa. The emission factors developed for the different recyclables in the country show savings varying from ?290 kg CO₂ e (glass) to ?19 111 kg CO₂ e (metals – Al) per tonne of recyclable. They also show that there is variability, with energy intensive materials like metals having higher GHG savings in South Africa as compared to other countries. This underlines the interrelation of the waste management system of a country/region with other systems, in particular with energy generation, which in South Africa, is heavily reliant on coal. This study also shows that composting of garden waste is a net GHG emitter, releasing 172 and 186 kg CO₂ e per tonne of wet garden waste for aerated dome composting and turned windrow composting, respectively. The paper concludes that these emission factors are facilitating GHG emissions modelling for waste management in South Africa and enabling local municipalities to identify best practice in this regard.     

Microwave inactivation of Escherichia coli in healthcare waste

Public healthcare wastes from the city of Ribeirão Preto, SP, Brazil, pre-sterilised in an autoclave, were inoculated with 5 × 10⁵ microorganisms of the species Escherichia coli in vegetative form for microwave processing on a laboratory scale. An analysis was made of the influence of radiation exposure time (15, 25, 30 and 40 min) and power per waste mass unit (60, 80 and 100 W/kg) on the percentage of inactivation of the microorganisms at an incoming waste moisture level of 50%. The experimental results were adjusted based on Chick’s law. The activation energies and the Arrhenius pre-exponential factors were determined by the least squares method. The kinetic parameters obtained allow one to predict the degree of inactivation achieved with E. coli in typical healthcare waste, based on the radiation exposure time and temperature. For example, the waste disinfection time required for the inactivation level equivalent to 4Log10 was estimated to range from 48 to 53 min for wastes processed at 100 W/kg and at temperatures of 90–105 °C, respectively. Thus, under the operational conditions of the equipment currently used in Ribeirão Preto, the process of inactivation is probably ineffective, since the exposure time to radiation is only 30 min at the average power of approximately 80 W/kg.     

A total quality management approach to healthcare waste management in Namazi Hospital,Iran

BackgroundHealthcare waste comprises all wastes generated at healthcare facilities, medical research centers and laboratories. Although 75–90% of these wastes are classified as household waste posing no potential risk, 10–25% are deemed to be hazardous, representing a potential threat to healthcare workers, patients, the environment and even the general population, if not disposed of appropriately. If hazardous and non-hazardous waste is mixed and not segregated prior to disposal, costs will increase substantially. Medical waste management is a worldwide issue. In Iran, the majority of problems are associated with an exponential growth in the healthcare sector together with low- or non-compliance with guidelines and recommendations. The aim of this study was to reduce the amounts of infectious waste by clear definition and segregation of waste at the production site in Namazi Hospital in Shiraz, Iran.Materials and methodsNamazi Hospital was selected as a study site with an aim to achieving a significant decrease in infectious waste and implementing a total quality management (TQM) method. Infectious and non-infectious waste was weighed at 29 admission wards over a 1-month period.ResultsBefore the introduction of the new guidelines and the new waste management concept, weight of total waste was 6.67 kg per occupied bed per day (kg/occupied bed/day), of which 73% was infectious and 27% non-infectious waste. After intervention, total waste was reduced to 5.92 kg/occupied bed/day, of which infectious waste represented 61% and non-infectious waste 30%. The implementation of a new waste management concept achieved a 26% reduction in infectious waste.ConclusionA structured waste management concept together with clear definitions and staff training will result in waste reduction, consequently leading to decreased expenditure in healthcare settings.     

Detailed internal characterisation of two Finnish landfills by waste sampling

The aim of this study was to characterise the internal structure and composition of landfilled waste at two Finnish landfills to provide information for active and post-landfill operations. The two sites, Ämmässuo and Kujala, have been in operation for 17 and 48 years, respectively. Waste was sampled (total 68 samples) and analysed for total solids (TS), volatile solids (VS), total Kjeldahl nitrogen (TKN), biological methane potential (BMP) and leaching of organic material (determined as chemical oxygen demand, COD) and ammonium nitrogen (NH₄–N). The results showed high vertical and horizontal variability, which indicated that both the waste composition and state of degradation varied greatly in both landfills. Ämmässuo was characterised by 2- to 4-fold higher BMP, NH₄–N and COD leaching than Kujala. Moreover, the ratio of VS to TS was higher at Ämmässuo, while TS content was lower. The highest mean BMPs (68 and 44 m³/t TS), TKN content (4.6 and 5.2 kg/t dry weight) and VS/TS ratio (65% and 59%) were observed in the middle and top layers; and the lowest mean BMP (21 and 8 m³/t TS), TKN content (2.4 kg/t dry weight, in both landfills) and VS/TS ratio (55% and 16% in Ämmässuo and Kujala, respectively) in the bottom layers. In conclusion, waste sampling is a feasible way of characterising the landfill body, despite the high variation observed and the fact that the minimum number and size of samples cannot easily be generalized to other landfills due to different methods of waste management and different landfilling histories.     

GHG emission factors developed for the collection,transport and landfilling of municipal waste in South African municipalities

Greenhouse gas (GHG) emission factors are used with increased frequency for the accounting and reporting of GHG from waste management. However, these factors have been calculated for developed countries of the Northern Hemisphere and are lacking for developing countries. This paper shows how such factors have been developed for the collection, transport and landfilling of municipal waste in South Africa. As such it presents a model on how international results and methodology can be adapted and used to calculate country-specific GHG emission factors from waste. For the collection and transport of municipal waste in South Africa, the average diesel consumption is around 5 dm³ (litres) per tonne of wet waste and the associated GHG emissions are about 15 kg CO₂ equivalents (CO₂ e). Depending on the type of landfill, the GHG emissions from the landfilling of waste have been calculated to range from ?145 to 1016 kg CO₂ e per tonne of wet waste, when taking into account carbon storage, and from 441 to 2532 kg CO₂ e per tonne of wet waste, when carbon storage is left out. The highest emission factor per unit of wet waste is for landfill sites without landfill gas collection and these are the dominant waste disposal facilities in South Africa. However, cash strapped municipalities in Africa and the developing world will not be able to significantly upgrade these sites and reduce their GHG burdens if there is no equivalent replacement of the Clean Development Mechanism (CDM) resulting from the Kyoto agreement. Other low cost avenues need to be investigated to suit local conditions, in particular landfill covers which enhance methane oxidation.     

Vermicomposting toilets, an alternative to latrine style microbial composting toilets, prove far superior in mass reduction, pathogen destruction, compost quality, and operational cost

Composting toilets aim to recycle excrement into safe, stable humus. Preceding this, low costs, low risks, and mass reduction should be ensured. Source separating vermicomposting toilets (SSVCs) outperformed mixed latrine microbial composting toilets (MLMCs) in all categories. MLMCs: incurred ten times greater operational costs; created 10x more operator exposure; employed no proven pathogen reduction mechanism since solid end-products averaged 71,000 ± 230,000 CFU/g (fecal-origin) Escherichia coli and 24 ± 5% total solids, consistently failed NSF/ANSI Standard 41; failed to reduce volatile solids compared to raw fecal matter; increased total contaminated dry mass by 274%, and produced alkaline end-product (8.0 ± 0.7) high in toxic free ammonia (Solvita® 2.6 ± 1.5). SSVCs have low maintenance costs and risks; adequate worm density for pathogen destruction (0.03 ± 0.04 g-worm/g-material); reduced E. coli 200 ± 244 CFU/g in neutral (7.4 ± 0.3), stable (60 ± 10% volatile solids), and mature (4 ± 0 Solvita® NH₃) end-product.     

Effect of nine years of animal waste deposition on profile distribution of heavy metals in Abeokuta,south-western Nigeria and its implication for environmental quality

Uncontrolled deposition of waste from animal farms is a common practice in south-western Nigeria, and the presence of heavy metals in soil constitutes environmental and health hazards by polluting the soil, ground water, adjoining streams and rivers. The study investigated the profile distribution of Mn, Pb, Cd, Zn, Fe, Cu, Ni and Cr in some tropical Alfisols in south-western Nigeria after nine years disposal of animal wastes. The amount of these metals in the soil horizons was high enough to cause health and phytotoxic risks. All the metals except Zn and Cr increased down the profile, while Mn, Pb, Cd, Fe, Cu and Ni accumulated at 80–120 cm depth. The increment of these metals at this depth over the top soil were 26%, 143%, 72%, 47%, 328% for Mn, Pb, Cd, Cu and Ni, respectively. It thus, shows their mobility and the possibility of polluting ground water. The Mn content at the poultry and cattle waste sites increased by 127% and 25%, respectively over the control, while that of cattle and swine dump site for Cd content were 9.82 and 15.63 mg kg^?1, respectively. Lead content also increased by 8.52 and 5.25 mg kg^?1, respectively.There was the accumulation of Zn and Cu at the swine dump site while the cattle dump site had the highest amounts of nickel and chromium. The least amount of Fe was recorded at the swine waste dump site. The reduction in organic matter with depths together with the reduced pH might have favored the mobility of the metals. The ranking of pollution among the sites was poultry > swine > cattle > sheep and could be due to the type of ration fed, the vaccination programmes, sanitation programmes and other management practices.     

The changing character of household waste in the Czech Republic between 1999 and 2009 as a function of home heating methods

The authors of this paper report on the changing character of household waste, in the Czech Republic between 1999 and 2009 in households differentiated by their heating methods. The data presented are the result of two projects, financed by the Czech Ministry of Environment, which were undertaken during this time period with the aim of focusing on the waste characterisation and complete analysis of the physicochemical properties of the household waste. In the Czech Republic, the composition of household waste varies significantly between different types of households based on the methods of home heating employed. For the purposes of these studies, the types of homes were divided into three categories – urban, mixed and rural. Some of the biggest differences were found in the quantities of certain subsample categories, especially fine residue (matter smaller than 20 mm), between urban households with central heating and rural households that primarily employ solid fuel such coal or wood. The use of these solid fuels increases the fraction of the finer categories because of the higher presence of ash. Heating values of the residual household waste from the three categories varied very significantly, ranging from 6.8 MJ/kg to 14.2 MJ/kg in 1999 and from 6.8 MJ/kg to 10.5 MJ/kg in 2009 depending on the type of household and season. The same factors affect moisture of residual household waste which varied from 23.2% to 33.3%. The chemical parameters also varied significantly, especially in the quantities of Tl, As, Cr, Zn, Fe and Mn, which were higher in rural households. Because knowledge about the properties of household waste, as well as its physicochemical characteristics, is very important not only for future waste management, but also for the prediction of the behaviour and influence of the waste on the environment as the country continues to streamline its legislation to the European Union’s solid waste mandates, the results of these studies were employed by the Czech Ministry of Environment to optimise the national waste management strategy.     

Sustainable sanitary landfills for neglected small cities in developing countries: The semi-mechanized trench method from Villanueva,Honduras

Open dumping is the most common practice for the disposal of urban solid wastes in the least developed regions of Africa, Asia and Latin America. Sanitary landfill design and operation has traditionally focused on large cities, but cities with fewer than 50,000 in population can comprise from 6% to 45% of a given country’s total population. These thousands of small cities cannot afford to operate a sanitary landfill in the way it is proposed for large cities, where heavy equipment is used to spread and compact the waste in daily cells, and then to excavate, transport and apply daily cover, and leachate is managed with collection and treatment systems. This paper presents an alternative approach for small cities, known as the semi-mechanized trench method, which was developed in Villanueva, Honduras. In the semi-mechanized trench method a hydraulic excavator is used for 1–3 days to dig a trench that will last at least a month before it is filled with waste. Trucks can easily unload their wastes into the trench, and the wastes compact naturally due to semi-aerobic biodegradation, after which the trenches are refilled and covered. The exposed surface area is minimal since only the top surface of the wastes is exposed, the remainder being covered by the sides and bottom of the trench. The surplus material from trench excavation can be valorized for use as engineering fill onsite or off. The landfill in Villanueva has operated for 15 years, using a total land area of approximately 11 ha for a population that grew from 23,000 to 48,000, with a land requirement of 0.2 m²/person year, a cover to waste ratio of 0.2, and an estimated soil surplus of 298,000 m³ that is valorized and used onsite. The landfill has been operated solely by the municipality with an operational cost in 2010 estimated at US$4.60 per ton. A modified water balance analysis at Villanueva shows negligible leachate generation from covered trenches and 700 m³/yr (60 m³/ha yr) from the two open trenches required for daily operation. If the site were an open dump, however, leachate generation is estimated to be 3900 m³/ha yr and contaminated runoff 5000 m³/ha yr. A simple model used to estimate dilution of generated leachate based on groundwater flow data and aquifer stratigraphy suggests that the leachate will be diluted by a factor of 0.01 in the aquifer. Leachate contaminants will not accumulate because the aquifer discharges to the Ulua River 2 km south of the landfill. While not suitable for all sites, the Villanueva method nevertheless serves as an excellent example of how a small city landfill with natural compaction of waste and attenuation of leachate can be sustainably operated.     

Seasonal generation and composition of garden waste in Aarhus (Denmark)

Garden waste generation and composition were studied in Aarhus, Denmark. The amount of garden waste generated varied seasonally, from 2.5 kg person^?1 month^?1 in winter to 19.4 kg person^?1 month^?1 in summer. Seasonal fractional composition and chemical characterization of garden waste were determined by sorting and sampling garden waste eight times during 1 year. On a yearly basis, the major fraction of garden waste was “small stuff” (flowers, grass clippings, hedge cuttings and soil) making up more than 90% (wet waste distribution) during the summer. The woody fractions (branches, wood) are more significant during the winter. Seasonal trends in waste chemical composition were recorded and an average annual composition of garden waste was calculated, considering the varying monthly generation and material fraction composition: the wet garden waste contained 40% water, 30% organic matter (VS) and 30% ash. The ash content suggests that the garden waste contains a significant amount of soil. This is in particular the case during summer. Of nutrients, the garden waste contained in average on a dry matter basis 0.6% N, 0.1% P, and 1.0% K. However, the contents varied significantly among the fractions and during the year. The content of trace elements (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) was low.     

Investigation of health care waste management in Binzhou District,China

In China, national regulations and standards for health care waste management were implemented in 2003. To investigate the current status of health care waste management at different levels of health care facilities (HCF) after the implementation of these regulations, one tertiary hospital, one secondary hospital, and four primary health care centers from Binzhou District were visited and 145 medical staff members and 24 cleaning personnel were interviewed.Generated medical waste totaled 1.22, 0.77, and 1.17 kg/bed/day in tertiary, secondary, and primary HCF, respectively. The amount of medical waste generated in primary health care centers was much higher than that in secondary hospitals, which may be attributed to general waste being mixed with medical waste. This study found that the level of the HCF, responsibility for medical waste management in departments and wards, educational background and training experience can be factors that determine medical staff members’ knowledge of health care waste management policy. Regular training programs and sufficient provision of protective measures are urgently needed to improve occupational safety for cleaning personnel. Financing and administrative monitoring by local authorities is needed to improve handling practices and the implementation of off-site centralized disposal in primary health care centers.     

Seasonal characterization of municipal solid waste (MSW) in the city of Chihuahua,Mexico

Management of municipal solid waste (MSW) has become a significant environmental problem, especially in fast-growing cities. The amount of waste generated increases each year and this makes it difficult to create solutions which due to the increase in waste generation year after year and having to identify a solution that will have minimum impact on the environment. To determine the most sustainable waste management strategy for Chihuahua, it is first necessary to identify the nature and composition of the city’s urban waste. The MSW composition varied considerably depending on many factors, the time of year is one of them. Therefore, as part of our attempt to implement an integral waste management system in the city of Chihuahua, we conducted a study of the characteristics of MSW composition for the different seasons. This paper analyzes and compares the findings of the study of the characterization and the generation of solid waste from households at three different socio-economic levels in the city over three periods (April and August, 2006 and January, 2007).The average weight of waste generated in Chihuahua, taking into account all three seasons, was 0.592 kg capita^?1 day^?1. Our results show that the lowest income groups generated the least amount of waste. We also found that less waste was generated during the winter season. The breakdown for the composition of the waste shows that organic waste accounts for the largest proportion (45%), followed by paper (17%) and others (16%).     

Applications of life cycle assessment and cost analysis in health care waste management

The establishment of rules to manage Health Care Waste (HCW) is a challenge for the public sector. Regulatory agencies must ensure the safety of waste management alternatives for two very different profiles of generators: (1) hospitals, which concentrate the production of HCW and (2) small establishments, such as clinics, pharmacies and other sources, that generate dispersed quantities of HCW and are scattered throughout the city. To assist in developing sector regulations for the small generators, we evaluated three management scenarios using decision-making tools. They consisted of a disinfection technique (microwave, autoclave and lime) followed by landfilling, where transportation was also included. The microwave, autoclave and lime techniques were tested at the laboratory to establish the operating parameters to ensure their efficiency in disinfection. Using a life cycle assessment (LCA) and cost analysis, the decision-making tools aimed to determine the technique with the best environmental performance. This consisted of evaluating the eco-efficiency of each scenario. Based on the life cycle assessment, microwaving had the lowest environmental impact (12.64 Pt) followed by autoclaving (48.46 Pt). The cost analyses indicated values of US$ 0.12 kg^?1 for the waste treated with microwaves, US$ 1.10 kg^?1 for the waste treated by the autoclave and US$ 1.53 kg^?1 for the waste treated with lime. The microwave disinfection presented the best eco-efficiency performance among those studied and provided a feasible alternative to subsidize the formulation of the policy for small generators of HCW.     

Determination of biogas generation potential as a renewable energy source from supermarket wastes

Fruit, vegetable, flower waste (FVFW), dairy products waste (DPW), meat waste (MW) and sugar waste (SW) obtained from a supermarket chain were anaerobically digested, in order to recover methane as a source of renewable energy. Batch mesophilic anaerobic reactors were run at total solids (TS) ratios of 5%, 8% and 10%. The highest methane yield of 0.44 L CH₄/g VS_added was obtained from anaerobic digestion of wastes (FVFW + DPW + MW + SW) at 10% TS, with 66.4% of methane (CH₄) composition in biogas. Anaerobic digestion of mixed wastes at 5% and 8% TS provided slightly lower methane yields of 0.41 and 0.40 L CH₄/g VS_added, respectively. When the wastes were digested alone without co-substrate addition, the highest methane yield of 0.40 L CH₄/g VS_added was obtained from FVFW at 5% TS. Generally, although the volatile solids (VS) conversion percentages seemed low during the experiments, higher methane yields could be obtained from anaerobic digestion of supermarket wastes. A suitable carbon/nitrogen (C/N) ratio, proper adjustment of the buffering capacity and the addition of essential trace nutrients (such as Ni) could improve VS conversion and biogas production yields significantly.     

Determination of plate waste in primary school lunches by weighing and visual estimation methods: A validation study

The aim of this study was to validate the visual estimation method for aggregated plate waste of main dish at Portuguese primary school canteens. For this purpose plate waste at school lunch was measured for 505 individual servings, using weighing individual servings and plate waste and visual estimation method by a 6-point scale, as developed by Comstock et al. (1981). A high variability of initial serving weights was found with serving sizes ranging from 88.9 to 283.3 g and with a coefficient of variation ranging from 5.5% to 24.7%. Mean plate waste was 27.5% according to the weighing method. There was a significant bias in the conversion of the visual waste estimations to actual waste, being overestimated by an average of 8.0 g (ranging from ?12.9 g to 41.4 g). According to Bland and Altman plot, the mean difference between methods was of 8.0 g and the amplitude interval was 102.6 g. The study showed that the visual estimation method is not as accurate as the weighing method in assessing nonselective aggregated plate waste at primary school canteens. Our findings are thus very important on considering plate waste assessment, since the wide variation on initial servings introduces a relevant bias when considering standard portions or a random sample of initial servings. Although, greater convenience, time-saving and the possibility to monitor plate waste of large groups, make the visual estimation method an important method to assess plate waste at school canteens, these results highlighted the need of portions standardization and control of initial servings to allow for its use.