Source-separated Household Waste Research Articles

Liquid digestate from anaerobic treatment of source-separated household waste as fertilizer to barley

This study examined the efficiency of different organic waste materials as NPK fertilizer, in addition to the risk for leaching losses related to shower precipitation in the first part of the growing season. The experiment was tested in a pot trial on a sandy soil in a greenhouse. Six organic fertilizers were evaluated: liquid anaerobic digestate (LAD) sourced from separated household waste, nitrified liquid anaerobic digestate (NLAD) of the same origin as LAD, meat and bone meal (MBM), hydrolysed salmon protein (HSP), reactor-composted catering waste (CW) and cattle manure (CM). An unfertilized control, calcium nitrate (CN) and Fullgjødsel® 21-4-10 were used as reference fertilizers. At equal amounts of mineral nitrogen both LAD and Fullgjødsel® gave equal yield of barley in addition to equal uptake of N, P, and K in barley grain. NLAD gave significantly lower barley yield than the original LAD due to leaching of nitrate-N after a simulated surplus of precipitation (28 mm) at Zadoks 14. There was significantly increased leaching of nitrate N from the treatments receiving 160 kg N ha(-1) of CN and NLAD in comparison with all the other organic fertilizers. In this study LAD performed to the same degree as Fullgjødsel® NPK fertilizer and it was concluded that LAD can be recommended as fertilizer for cereals. Nitrification of the ammonium N in the digestate caused significantly increased nitrate leaching, and cannot be recommended.

Land application of organic waste – Effects on the soil ecosystem

Growing populations and the increasing use of existing resources has led to growth in organic waste emissions. Therefore, a sustainable approach to managing this waste has become a major concern in densely populated areas. Biological treatment is an efficient method for reducing the amount of organic waste, and for producing energy. A large number of biogas plants and compost facilities that use organic waste as a substrate for electricity and fuel production are being built around the world. The biological treatment process in these plants produces large amounts of organic waste, and there is therefore a growing need to find a sustainable use for this material. Organic waste, such as biogas residues and compost can be a valuable fertilizer for agricultural soils. They can serve as a source of plant nutrients and can also improve soil structure and water holding capacity. However, as organic residues are known to contain both heavy metals and organic contaminants there is a need for long term field experiments to ensure that soil and plant quality is maintained. In order to investigate the potential risks and benefits of using organic waste in agriculture, an 8 year field experiment was established in central Sweden. Under realistic conditions, compost and biogas residues from source-separated household waste were compared with traditional mineral fertilizer. We examined crop yield and soil chemical and microbiological properties. The main conclusion from the field experiment was that biogas residues resulted in crop yields almost as high as the mineral fertilizer NPS. In addition, several important soil microbiological properties, such as substrate induced respiration, potential ammonium oxidation and nitrogen mineralization were improved after application of both biogas residues and compost. Moreover, no negative effects could be detected from using either of the organic wastes. In particular the genetic structure of the soil bacterial community appeared to resist changes caused by addition of organic waste.

Current-use and Organochlorine Pesticides and Polychlorinated Biphenyls in the Biodegradable Fraction of Source Separated Household Waste, Compost, and Anaerobic Digestate

Several current-use (≤ 80 ng g⁻¹ dry weight) and organochlorine pesticides (≤ 15 ng g⁻¹ dry weight) and polychlorinated biphenyls (≤ 18 ng g⁻¹ dry weight) were found in the biodegradable fraction of source separated household waste, compost, and/or anaerobic digestate. The degradation rates of individual compounds differ depending on the treatment. Dieldrin and pentachloroaniline, e.g., degrade more rapidly than the waste is mineralized and accumulates in the products after all treatments. Many organochlorines degrade at the same rate as the waste and have the same concentrations in the waste and products. Chlorpyrifos degrades slower than the waste and accumulates in all products and ethion during anaerobic digestion. The polychlorinated biphenyls and some pesticides show different degradations rates relative the waste during different processes. Understanding the degradation of the contaminants under different conditions is necessary to develop quality criteria for the use of compost and digest.

Characterisation of source-separated household waste intended for composting

Large-scale composting of source-separated household waste has expanded in recent years in the Nordic countries. One problem can be low pH at the start of the process. Incoming biowaste at four composting plants was characterised chemically, physically and microbiologically. The pH of food waste ranged from 4.7 to 6.1 and organic acid concentration from 24 to 81 mmol kg−1. The bacterial diversity in the waste samples was high, with all samples dominated by Gammaproteobacteria, particularly Pseudomonas and Enterobacteria (Escherichia coli, Klebsiella, Enterobacter). Lactic acid bacteria were also numerically important and are known to negatively affect the composting process because the lactic acid they produce lowers the pH, inhibiting other bacteria. The bacterial groups needed for efficient composting, i.e. Bacillales and Actinobacteria, were present in appreciable amounts. The results indicated that start-up problems in the composting process can be prevented by recycling bulk material and compost.

Effect of wood fly ash and compost on nitrification and denitrification in agricultural soil

Wood ash from biofuel combustion plants and compost from source-separated household waste are commonly spread on forest, agricultural and horticultural soils as a valuable source of plant nutrients. However, due to anthropogenic activities, wood ash may contain high concentrations of heavy metals. Heavy metals are toxic to microorganisms and therefore, soil microbial response to wood ash should be considered when soil is amended with ash. Compost is known to improve soil structure and may also act as a bioremediating agent, mitigating any toxic effects of wood ash on soil microorganisms. In the present study, the aim was to investigate whether wood ash has any toxic effect on soil microbial activity and, if this is the case, whether compost could mitigate these effects. The effect of wood fly ash on potential ammonium oxidation rate (PAO) and potential denitrification rate (PDA) in arable soil was investigated in one dose–response assay and in two pot experiments with or without plants, respectively. The treatments were amendment with wood fly ash, compost or a combination of wood fly ash and compost. PAO and PDA were assessed immediately or after 7 and 90 days in the different experiments. Wood fly ash decreased PDA to 16–56% compared to the control, while PAO varied between 82% and 205%. Sole compost addition stimulated both processes. This positive effect was also observed in the combined wood fly ash–compost treatment. In conclusion, wood ash had a toxic effect on PDA, both on an immediate, short-term and long-term basis. Amendment of compost clearly mitigated this toxic effect. The observed toxicity could be an effect of the metal content of ash.

Carbon Turnover and Ammonia Emissions during Composting of Biowaste at Different Temperatures

The effects of different process temperatures (40, 55, and 67 degrees C) during composting of source-separated household waste were studied in a 200 L compost reactor at an oxygen concentration of 16%. The overall decomposition measured as carbon mineralization, decomposition of different carbon constituents, and the dynamics of nitrogen mineralization and the microbial community, are reported. Ammonia emissions at 67 degrees C were more than double those at lower temperatures, and they were lowest at 40 degrees C. The decomposition rate, measured as CO2 emission, was highest at 55 degrees C. Decomposition of crude fat was slower at 40 degrees C than at 55 and 67 degrees C. The peak in microbial biomass was largest in the run at 40 degrees C, where substantial differences were seen in the microbial community structure and succession compared to thermophilic temperatures. Biowaste composting can be optimized to obtain both a high decomposition rate and low ammonia emissions by controlling the process at about 55 degrees C in the initial, high-rate stage. To reduce ammonia emissions it seems worthwhile to reduce the temperature after an initial high-temperature stage.

Evaluation of environmental impacts from municipal solid waste management in the municipality of Aarhus, Denmark (EASEWASTE)

A new computer based life cycle assessment model (EASEWASTE) was used to evaluate a municipal solid waste system with the purpose of identifying environmental benefits and disadvantages by anaerobic digestion of source-separated household waste and incineration. The most important processes that were included in the study are optical sorting and pre-treatment, anaerobic digestion with heat and power recovery, incineration with heat and power recovery, use of digested biomass on arable soils and finally, an estimated surplus consumption of plastic in order to achieve a higher quality and quantity of organic waste to the biogas plant. Results showed that there were no significant differences in most of the assessed environmental impacts for the two scenarios. However, the use of digested biomass may cause a potential toxicity impact on human health due to the heavy metal content of the organic waste. A sensitivity analysis showed that the results are sensitive to the energy recovery efficiencies, to the extra plastic consumption for waste bags and to the content of heavy metals in the waste. A model such as EASEWASTE is very suitable for evaluating the overall environmental consequences of different waste management strategies and technologies, and can be used for most waste material fractions existing in household waste.

The fertilizing effect of compost and biogas residues from source separated household waste

In Sweden, deposition of organic waste will be prohibited in the year 2005. Instead, the waste will be either incinerated or source separated, processed (composted or anaerobically digested) and recycled back to arable land. In order to evaluate the biologically processed waste products as fertilizers, a field experiment was initiated in Sweden in the autumn of 1998. The main focus of the experiment was to compare compost (C) from source-separated domestic waste with biogas residues (BR) from source-separated domestic waste. Each fertilizer was applied in two combinations: in treatments C50 and BR50, 50 kg N/ha/year originates from the waste and 50 kg N/ha/year from mineral nitrogen fertilizer, while in C100 and BR100, the organic wastes were the only plant nutrient sources (100 kg N/ha/year). Mineral fertilizer (NPS100) and unamended were used as controls. Generally pure mineral fertilizers resulted in the highest yield, while control without nitrogen generated the lowest yield. A combination of organic fertilizer and mineral fertilizer resulted in higher yield compared with applying sole organic fertilizer. Total mineral N in the fertilizer was generally the best overall predictor/regressor for grain yield, total nitrogen yield and apparent bioavailable nitrogen. Application of biogas residue resulted in higher yield and grain quality than compost. The higher concentration of nitrogen in oats suggested that oats is a better choice when using compost as a fertilizer. In conclusion, compost and anaerobic biogas residues should not be used as sole fertilizers. Compost should be complemented with mineral N and the biogas residues with P. If compensation for the low content of mineral N in compost is made by a higher application rate, large amounts of heavy metals might be applied along with the compost.

Pressurized-fluid extraction (PFE) of chlorinated paraffins from the biodegradable fraction of source-separated household waste.

A method is presented in which pressurized-fluid extraction (PFE) is used for the extraction of chlorinated paraffins (CP) from the biodegradable fraction of source-separated household waste. The conditions that were optimized for high recovery in the extraction procedure were extraction time, temperature, and the use of different solvents and different sample particle sizes, Recoveries of CP from fortified household waste material were over 90%, with only few interferences when cyclohexane was used as solvent. Extraction yields from contaminated samples containing CP were further compared with recoveries obtained by use of Soxtec extraction. The results showed that PFE is a rapid, low-solvent-consuming technique, giving high yields.

Systemic Resistance Induced in Cucumber Against Pythium Root Rot by Source Separated Household Waste And Yard Trimmings Composts

Disease control with compost often is attributed to four factors including competition, antibiosis, parasitism and induced systemic resistance (ISR). Induction of systemic resistance by source separated household waste and yard trimmings compost against Pythium root rot of cucumber caused by Pythium ultimum was studied in a split-root bioassay. Split-root pairings were tested in root rot potting soil paired with potting soil, compost-amended potting soil suppressive to root rot paired with the potting soil, and compost-amended potting soil paired with the compost-amended potting soil. Only one side of the split roots was infested with P. ultimum. Root rot, based on dry and fresh root weights, was significantly reduced in split roots of plants produced in the conducive infested potting soil paired with the suppressive yard trimmings compost-amended mix. This suggested that systemic effects were induced in the roots by the suppressive compost against Pythium root rot. Growth of transplants germinated in the source separated household waste compost mix was significantly better than those germinated in the potting soil. Finally, root rot of plants germinated in the suppressive mix and then transplanted into the conducive mix was also significantly less severe than that of plants germinated in the conducive mix.