Recovery of essential nutrients from municipal solid waste--Impact of waste management infrastructure and governance aspects

Closing the nutrient cycle in urban areas: The use of municipal solid waste in peri-urban and urban agriculture

Cities face the challenges of supplying food and managing organic municipal solid waste (OMSW) sustainably amid increasing urbanization rates. Urban agriculture (UA) can help with this effort by producing local crops that are fertilized with nutrients recovered from compost generated from OMSW. This research aims to determine the potential of OMSW compost to supply the nitrogen-phosphorus-potassium (NPK) demand of UA and the environmental benefits of replacing mineral fertilizer from a life cycle perspective. The Metropolitan Area of Barcelona (AMB) serves as the case study given its commitment to reuse biowaste according to the Revised Waste Framework Directive and to promote UA as a signing member of the Milan Urban Food Policy Pact. Based on crop requirements and farmer surveys, we find that the annual NPK demands of the agricultural fields of the AMB that cover 5,500 ha and produce 70,000 tons of crops are approximately 769, 113, and 592 tons of NPK, respectively. Spatial material flow analysis and life cycle assessment were applied to found that the current waste management system can potentially substitute 8 % of the total NPK demanded by UA with compost, reduce the impacts by up to 39 % and yield savings in global warming of 130 %. The more ambitious future scenario of 2025 can potentially substitute 21 % of the total NPK demand and reduce environmental impacts up to 1,049 %, depending on the category considered. Avoiding processing of mixed OMSW, mineral fertilizer replacement and cogeneration of electricity from biogas are the major contributors to these environmental savings.

Evaluation of the effect of a novel substrate that is composed of landfill-mined-soil-like-fractions on plant growth and heavy metal accumulation

In the pursuit of a safe, low-cost, and sustainable method for the reuse of landfill-mined-soil-like-fractions (LFMSFs), pot experiments were conducted using seven growth substrates consisting of LFMSFs, tea residue, and peat for the cultivation of Photinia × fraseri. Six of the substrates had 40 %:60 %, 60 %:40 %, and 80 %:20 % volume ratios of LFMSFs to tea residue or peat, and one substrate consisted entirely of LFMSFs. The physicochemical properties of the substrate, growth parameters of the plants, and heavy metal content in the different pots were determined after one year of growth. The results indicated that the physicochemical properties of the substrate, that was composed of a mixture of LFMSFs and tea residue showed a significant improvement in organic matter, nitrogen, phosphorus, and potassium. However, there was also an increase in the salt and heavy metal contents when compared with those of peat. The plant growth in the LFMSF and tea residue substrate was slightly lower than that in the LFMSF and peat mixture. Notably, the best plant growth and environmentally friendly effects were observed when LFMSFs were added at 40 %. Additionally, most of the heavy metals were primarily removed from the substrate through the leaves of the seedlings, with the heavy metal contents being relatively low. In conclusion, LFMSFs as a cultivation substrate, represent a practical approach for reutilization, which could contribute to the reduction of reliance on traditional resources.

Literature review on the potential of urban waste for the fertilization of urban agriculture: A closer look at the metropolitan area of Barcelona

Urban agriculture (UA) activities are increasing in popularity and importance due to greater food demands and reductions in agricultural land, also advocating for greater local food supply and security as well as the social and community cohesion perspective. This activity also has the potential to enhance the circularity of urban flows, repurposing nutrients from waste sources, increasing their self-sufficiency, reducing nutrient loss into the environment, and avoiding environmental cost of nutrient extraction and synthetization. The present work is aimed at defining recovery technologies outlined in the literature to obtain relevant nutrients such as N and P from waste sources in urban areas. Through literature research tools, the waste sources were defined, differentiating two main groups: (1) food, organic, biowaste and (2) wastewater. Up to 7 recovery strategies were identified for food, organic, and biowaste sources, while 11 strategies were defined for wastewater, mainly focusing on the recovery of N and P, which are applicable in UA in different forms. The potential of the recovered nutrients to cover existing and prospective UA sites was further assessed for the metropolitan area of Barcelona. Nutrient recovery from current composting and anaerobic digestion of urban sourced organic matter obtained each year in the area as well as the composting of wastewater sludge, struvite precipitation and ion exchange in wastewater effluent generated yearly in existing WWTPs were assessed. The results show that the requirements for the current and prospective UA in the area can be met 2.7 to 380.2 times for P and 1.7 to 117.5 times for N depending on the recovery strategy. While the present results are promising, current perceptions, legislation and the implementation and production costs compared to existing markets do not facilitate the application of nutrient recovery strategies, although a change is expected in the near future.

The impact of public awareness, infrastructure, and technological development with economic growth on solid waste management of European countries: does governance quality matters

Solid waste generation is a significant problem affecting the ecosystem, human health, and safety. However, the issue is not given the attention it truly deserves. Consequently, this study is aimed at assessing the impact of various factors, such as economic growth, public awareness, infrastructure, and technological advancements, on generating municipal waste in the European Union (EU) for the period 1995-2020. Furthermore, the study incorporated the mediating effect of economic growth and government effectiveness with public awareness, infrastructure, and technological development to reduce waste generation. By employing the bias-corrected method of moments, the study finds that overall waste generation does not decrease over time in EU economies. Furthermore, Denmark is the top-ranked country among the sampled countries to generate waste. However, Finland is at the top in government effectiveness. The empirical findings showed that economic growth is the significant reason for the increase in solid waste production. Additionally, the interaction effects of economic growth with public awareness, infrastructure, and technological development are positive. However, the individual impact of public awareness, infrastructure, and technological development is positive in reducing waste generation. Governance effectiveness is a significant tool to lower waste generation in European economies.

Sequential treatment of nitrate and phosphate in groundwater using a permeable reactive barrier system

When not properly treated, nitrate and phosphate present in groundwater can damage human health and environments. In this study, laboratory column experiments were performed for sequential treatment of nitrate and phosphate in groundwater. Two columns were set up and connected: one to treat nitrate with organic carbon materials (i.e., woodchips) and the other to treat phosphate with basic oxygen furnace (BOF) slag. The columns were operated for a total of 1.6 years. The results showed that nitrate was removed through denitrification and phosphate was removed by precipitation of the phosphate minerals (e.g., hydroxyapatite). BOF slag was effective at removing phosphate, though the high pH (11-12) of the system's effluent water raised a concern for the downgradient areas. Of the three subsequent experiments performed, pH was near neutral when the effluent of the BOF slag column was passed through local soil. Sparging with CO₂ and air, in contrast, resulted in pH levels that were either too low (5 in the case of CO₂) or too high (9.5 in the case of air). The study shows that sequential permeable reactive barrier (PRB) systems consisting of woodchips and BOF slag can be effective for removal of nitrate and phosphate in groundwater and they can be a long-term remedial solution for groundwater contaminated with both nitrate and phosphate.

Material Flow Analysis (MFA) and waste characterizations for formal and informal performance indicators in Tandil, Argentina: Decision-making implications

In cities, the achievement of waste-related legal requirements and the main drivers of Integrated Sustainable Waste Management (ISWM) need adequate indicators and adaptable-to-case tools and strategies. In this work, we combine Material Flow Analysis (MFA) and waste characterizations to develop a mass balance table to design, calculate and analyse indicators related to the formal and informal waste sub-circuits of Tandil, a medium-sized city of the Buenos Aires province (Argentina). Results show that global recovery is very low (2.3% ± 0.16) and mainly driven by the Informal Recovery Sector (IRS). Also, the IRS strategy is more effective, recovering 40% ± 8.0 of its targeted materials from non-household sources. Regarding each material recovery performance, results show significant differences. For paper and board, recovery exceeds 20%. For HDPE, Tetra brik and Ferrous Metals are lower than 1%. In the case of PET and Glass, 9.6 and 9.0% of what is generated in households is recovered, respectively. However, the global recovery rate of each material is different: 2.9% ± 0.4 for PET and 5.5% ± 1.4 for Glass. Our research show that strategies in place are insufficient regarding legislation in force. Even a hypothetically 100% effectiveness in them will account only for 20.9% ± 2.1 of global recovery. Addressing organic waste, therefore, is imperative. Considering the current province law provision of final disposal diversion, accounting for the work of the IRS is key because they recover more waste than the official strategy. Regarding open dumps eradication, we estimate that up to 17% of generated waste is incorrectly final disposed through private skips illegally dumped. A tracking system for skips could avoid this situation.

Application of artificial neural network and multiple linear regression in modeling nutrient recovery in vermicompost under different conditions

Vermicomposting is one of the best technologies for nutrient recovery from solid waste. This study aims to assess the efficiency of Artificial Neural Network (ANN) and Multiple Linear Regression (MLR) models in predicting nutrient recovery from solid waste under different vermicompost treatments. Seven chemical and biological indices were studied as input variables to predict total nitrogen (TN) and total phosphorus (TP) recovery. The developed ANN and MLR models were compared by statistical analysis including R-squared (R²), Adjusted-R², Root Mean Square Error and Absolute Average Deviation. The results showed that vermicomposting increased TN and TP proportions in final products by 1.5 and 16 times. The ANN models provided better prediction for TN and TP with R² of 0.9983 and 0.9991 respectively, compared with MLR models with R² of 0.834 and 0.729. TN and C/N ratio were key factors for TP and TN prediction by ANN with percentages of 17.76 and 18.33.

Bio-based fertilizers: A practical approach towards circular economy

Although for the past 100 years, fertilizer technologies have increasingly used renewable resources, the majority of manufactured products are still based on mineral deposits and fossil fuels. The European Commission has set a goal of 30% reduction of non-renewable resources in fertilizer production. This can only be accomplished if there are incentives for wastes valorization and fines for making use of non-renewable raw materials. This will enable the reduction of eutrophication of surface waters due to the presence of nitrogen and phosphorus, originating from agricultural fields fertilizers. The use of biological waste is a practical solution to recover valuable fertilizer components. In order to effectively implement technologies based on biological resources, it is necessary to construct small wastes solubilization or fertilizer installations at the site of waste generation, which will solve the problem of waste transport or sanitary hazards.

The role of management instruments in the diversion of organic municipal solid waste and phosphorus recycling

Organic waste, which contains essential plant nutrients such as phosphorus, constitutes 30%–50% of municipal solid waste in developed countries. Unfortunately, much of this resource is buried in landfills or incinerated. Many jurisdictions have, therefore, adopted the diversion of organic waste and the recycling of nutrients as policy goals. We used data sets from Europe and Ontario, Canada, to explore the impact of socio-economic and management factors on the rates of organic waste diversion and examined the effect of this diversion on phosphorus recycling. Organic diversion rates were highly correlated with income in Europe and with infrastructure, such as source-separated organic waste collection, in Ontario. Significant correlations were also observed between diversion rates and the use of policy instruments such as economic incentives, legislative organic waste bans, and curbside bag limits. We estimated that 39%–63% of the phosphorus in diverted organics is returned to arable land. Ultimately, we found that although socio-economic factors influence the success of organic waste diversion, policies, accessible infrastructure, economic incentives, and legislative requirements can be leveraged to improve the recycling rate of organic waste and the nutrients they contain.

Assessment of the municipal solid waste management system in Accra, Ghana: A 'Wasteaware' benchmark indicator approach

This article assesses the performance of the city of Accra, Ghana, in municipal solid waste management as defined by the integrated sustainable waste management framework. The article reports on a participatory process to socialise the Wasteaware benchmark indicators and apply them to an upgraded set of data and information. The process has engaged 24 key stakeholders for 9 months, to diagram the flow of materials and benchmark three physical components and three governance aspects of the city's municipal solid waste management system. The results indicate that Accra is well below some other lower middle-income cities regarding sustainable modernisation of solid waste services. Collection coverage and capture of 75% and 53%, respectively, are a disappointing result, despite (or perhaps because of) 20 years of formal private sector involvement in service delivery. A total of 62% of municipal solid waste continues to be disposed of in controlled landfills and the reported recycling rate of 5% indicates both a lack of good measurement and a lack of interest in diverting waste from disposal. Drains, illegal dumps and beaches are choked with discarded bottles and plastic packaging. The quality of collection, disposal and recycling score between low and medium on the Wasteaware indicators, and the scores for user inclusivity, financial sustainability and local institutional coherence are low. The analysis suggests that waste and recycling would improve through greater provider inclusivity, especially the recognition and integration of the informal sector, and interventions that respond to user needs for more inclusive decision-making.

Does recyclable separation reduce the cost of municipal waste management in Japan?

Municipal solid waste (MSW) management is a system involving multiple sub-systems that typically require demanding inputs, materials and resources to properly process generated waste throughput. For this reason, MSW management is generally one of the most expensive services provided by municipalities. In this paper, we analyze the Japanese MSW management system and estimate the cost elasticity with respect to the waste volumes at three treatment stages: collection, processing, and disposal. Although we observe economies of scale at all three stages, the collection cost is less elastic than the disposal cost. We also examine whether source separation at home affects the cost of MSW management. The empirical results show that the separate collection of the recyclable fraction leads to reduced processing costs at intermediate treatment facilities, but does not change the overall waste management cost. Our analysis also reveals that the cost of waste management systems decreases when the service is provided by private companies through a public tender. The cost decreases even more when the service is performed under the coordination of adjacent municipalities.