Marga López

An assessment of the characteristics of yard trimmings and recirculated yard trimmings used in biowaste composting.

The aim of this research was to characterise samples of yard trimmings (YT) and recirculated yard trimmings (RYT) that are used to co-compost organic fraction of municipal solid waste (OFMSW) taken from 18 composting facilities in Catalonia (NE Spain), to determine their contribution in the composting process, and to highlight the advantages and disadvantages of reusing RYT. We found significant differences between the characteristics of the two materials. RYT had higher pH levels, electrical conductivity, and organic and ammonium nitrogen content than YT. Nutrient content also shows an increment from YT to RYT, and in the case of P and K, this variation can be attributed to an exogenous source rather than the relative concentration during the composting process. We also found significant differences in particle size distribution and bulk density. From the results, it can be assumed that RYT could be reused in the composting process if OFMSW, YT, and RYT are used in the correct quantities to balance the mixture but they cannot totally replace the features of YT.

Bulk density determination as a simple and complementary tool in composting process control.

Ten composting facilities (CF) treating source-sorted organic fraction of municipal solid waste (OF) were sampled to study the relationship between the bulk density and the composting process (CP) development. Hundred and fourteen samples from different stages of the CP were considered (organic fraction, initial mixture, final decomposition, final maturation and compost), including the reject materials coming from the densimetric table at postprocessing. Total organic matter (TOM), moisture content (MC), wet bulk density and dry basis (BDd) were determined. Significant differences were detected for MC, TOM and BDd between some stages of the CP. The BDd increased along the CP while TOM decreased. Correlation studies showed a significant negative relationship between TOM and bulk density, especially BDd, during the CP, as a result of the biological activity. Moreover, a clear relationship was also found between TOM and BDd in samples related to reject materials. The results indicate that bulk density could be a simple and useful tool to evaluate the CP, in addition to the others parameters commonly used. At the same time, BDd could be an easy way to infer TOM lost within rejects.

Heavy metal content in rubbish bags used for separate collection of biowaste

The heavy metal content of several rubbish bags used to collect the organic fraction of municipal solid waste (OFMSW) is shown in this paper. Nowadays, several public awareness campaigns carried out by municipalities have promoted rubbish bags based mainly on their appearance, without concern for their heavy metal content. A high amount of heavy metals was detected in some polyethylene bags promoted in different campaigns for OFMSW source-sorted collection, while compostable bags presented low quantities of heavy metals. Some other rubbish bags, as well as commercial bags, were also analysed for comparison. These results should be taken into account before promoting the use of one or other type of bag. Moreover, the rubbish bag manufacturers should reduce the heavy metal content in order to avoid heavy metal scattering in the environment, and also to reduce the consumption of raw materials.

Nitrification during extended co-composting of extreme mixtures of green waste and solid fraction of cattle slurry to obtain growing media

Next generation of waste management systems should apply product-oriented bioconversion processes that produce composts or biofertilisers of desired quality that can be sold in high priced markets such as horticulture. Natural acidification linked to nitrification can be promoted during composting. If nitrification is enhanced, suitable compost in terms of pH can be obtained for use in horticultural substrates. Green waste compost (GW) represents a potential suitable product for use in growing medium mixtures. However its low N provides very limited slow-release nitrogen fertilization for suitable plant growth; and GW should be composted with a complementary N-rich raw material such as the solid fraction of cattle slurry (SFCS). Therefore, it is important to determine how very different or extreme proportions of the two materials in the mixture can limit or otherwise affect the nitrification process. The objectives of this work were two-fold: (a) To assess the changes in chemical and physicochemical parameters during the prolonged composting of extreme mixtures of green waste (GW) and separated cattle slurry (SFCS) and the feasibility of using the composts as growing media. (b) To check for nitrification during composting in two different extreme mixtures of GW and SFCS and to describe the conditions under which this process can be maintained and its consequences. The physical and physicochemical properties of both composts obtained indicated that they were appropriate for use as ingredients in horticultural substrates. The nitrification process occurred in both mixtures in the medium-late thermophilic stage of the composting process. In particular, its feasibility has been demonstrated in the mixtures with a low N content. Nitrification led to the inversion of each mixtures initial pH.

Development of organic fertilizers from food market waste and urban gardening by composting in Ecuador

Currently, the management of urban waste streams in developing countries is not optimized yet, and in many cases these wastes are disposed untreated in open dumps. This fact causes serious environmental and health problems due to the presence of contaminants and pathogens. Frequently, the use of specific low-cost strategies reduces the total amount of wastes. These strategies are mainly associated to the identification, separate collection and composting of specific organic waste streams, such as vegetable and fruit refuses from food markets and urban gardening activities. Concretely, in the Chimborazo Region (Ecuador), more than 80% of municipal solid waste is dumped into environment due to the lack of an efficient waste management strategy. Therefore, the aim of this study was to develop a demonstration project at field scale in this region to evaluate the feasibility of implanting the composting technology not only for the management of the organic waste fluxes from food market and gardening activities to be scaled-up in other developing regions, but also to obtain an end-product with a commercial value as organic fertilizer. Three co-composting mixtures were prepared using market wastes mixed with pruning of trees and ornamental palms as bulking agents. Two piles were created using different proportions of market waste and prunings of trees and ornamental palms: pile 1 (50:33:17) with a C/N ratio 25; pile 2: (60:30:10) with C/N ratio 24 and pile 3 (75:0:25) with C/N ratio 33), prepared with market waste and prunings of ornamental palm. Throughout the process, the temperature of the mixtures was monitored and organic matter evolution was determined using thermogravimetric and chemical techniques. Additionally, physico-chemical, chemical and agronomic parameters were determined to evaluate compost quality. The results obtained indicated that all the piles showed a suitable development of the composting process, with a significant organic matter decomposition, reached in a shorter period of time in pile 3. At the end of the process, all the composts showed absence of phytotoxicity and suitable agronomic properties for their use as organic fertilizers. This reflects the viability of the proposed alternative to be scaled-up in developing areas, not only to manage and recycle urban waste fluxes, but also to obtain organic fertilizers, including added value in economic terms related to nutrient contents.

Intelligent composting assisted by a wireless sensing network

Monitoring of the moisture and temperature of composting process is a key factor to obtain a quality product beyond the quality of raw materials. Current methodologies for monitoring these two parameters are time consuming for workers, sometimes not sufficiently reliable to help decision-making and thus are ignored in some cases. This article describes an advance on monitoring of composting process through a Wireless Sensor Network (WSN) that allows measurement of temperature and moisture in real time in multiple points of the composting material, the Compo-ball system. To implement such measurement capabilities on-line, a WSN composed of multiple sensor nodes was designed and implemented to provide the staff with an efficient monitoring composting management tool. After framing the problem, the objectives and characteristics of the WSN are briefly discussed and a short description of the hardware and software of the networks components are presented. Presentation and discussion of practical issues and results obtained with the WSN during a demonstration stage that took place in several composting sites concludes the paper.

Agroindustrial compost as a peat alternative in the horticultural industry of Ecuador

This work was conducted in order to investigate the possibility of using different agroindustrial composts in the production of horticultural seedlings, thereby replacing part of the peat in the growing media. Three vegetable species differing in salt sensitivity - tomato (Solanum lycopersicum L. var. Malpica) (the least sensitive), courgette (Cucurbita pepo L. var. Mastil F1) (moderately sensitive) and pepper (Capsicum annuum L. var. Largo de Reus Pairal) (the most sensitive) - were grown in nine media containing three composts, prepared by co-composting vegetable waste (flower, broccoli or tomato waste) with laying hen manure and sawdust, as well as peat in various ratios. The proportions of the three composts in the mixtures elaborated with peat were 25%, 50% and 75% (v/v). A substrate of 100% peat was used as control. The experiment was arranged in a completely-randomised design, with two replicates per treatment, under greenhouse conditions. Prior to sowing, some physical, physico-chemical and chemical properties of the growing media were determined and the seed germination and fresh and dry weights of the aerial parts and roots of the seedlings were also measured, as well as the mineral composition of the aerial parts of the plants. In most cases, the addition of compost to the growing media produced an increase in the pH, salt content and macronutrient concentrations, in comparison to peat, whereas the physical properties of the compost based-substrates had values very similar to those of an ideal substrate. Also, multivariate analysis showed that the media prepared with flower waste compost, at all concentrations, and the medium with tomato waste compost at 25% were the most suitable substrates for the three plant species tested.