Collection and Composting of Organic Waste: A Case Study In the City of Beira, Mozambique

Waste management has become one of the most complex and central environmental chal- lenges of the 21st century. Municipal solid waste (MSW) represents a threat not only to the environment but also to people’s health, especially in large cities in low-income contexts affected by uncontrolled urbanisation where the number of inhabitants is growing rapidly. MSW management and disposal practices vary significantly by income level, region and country development [1-11]. About 93% of waste is burned or dumped in lower-income countries [12-17]. Although more than 40% of the waste in the sub-Saharan Africa region is organic (OFMSW), only less of 1% is composted [18-20]. National and municipal govern- ments often have insufficient capacity or funding to meet the growing demand for MSW management services [21-23]. Therefore, especially in big cities, dumping of OFMSW is a more common practice than separating and sending it to a dedicated collection and valorisa- tion stream, despite the latter being the better option.

Mozambique ranks low on the human development index at 0.456, or 181 out of 189 countries [24], [25]. While the economy registered its first contraction in 2020 in nearly three decades, growth is expected to rebound over the medium-term, reaching about 4% by 2022 [26]. Since its recent independence from Portugal in 1975, agriculture as a pillar of the economy is suffering from the consequences of alternating natural events such as droughts, floods and cyclones [27].

With a population of 673,685 [28], Beira is the second main populated city of Mozam- bique. The city is the capital of Sofála Province in central Mozambique and has a geographi- cally unfavourable position, due to the many tropical cyclones that attack the Mozambican coast. The situation, also due to global warming, is not likely to improve, so it is necessary to make the city as safe as possible, including in terms of MSW management [29-31]. The heavy rains in the summertime can stagnate for days on the ground, creating large swamps even where there are open dumps. As a result, the waste is more widely dispersed and the leachate generated infiltrates the soil, reaching the groundwater and contaminating it.

The OFMSW is the biggest fraction in the MSW, and its decomposition in the case of uncontrolled destination (e.g., in dumpsites) can create problems of processing, odour, biogas and leachate, leading to pollution problems and costly environmental restoration [32-35]. That is why it is essential to correctly dispose this waste fraction by directing it to a dedicated treatment: composting, anaerobic digestion, etc [36-40].

Mozambique Environment Programme started in 2018 from the collaboration between two Italian NGOs (Progettomondo and CAM) and the municipalities of the two Mozambican cities: Beira and Nampula, following previous sector studies on MSW characterisation in collaboration with University of Trento and Fondazione Edmund Mach (research, educa- tion, and consultancy in agricultural, agri-food, and environmental sectors) [36]. Accelerated growth of cities, increase in consumer goods, low diffusion of collection services, low aware- ness and low technical-management capacity are some of the factors that show the need for urgent and systemic interventions aimed at mitigating the impact on environment and public health.

This five-year programme includes the LimpaMOS MOÇambique project, mainly co- financed by the Italian Agency for Development Cooperation. The project aims to strengthen the public institution in its material and human components, searching for sustainable and integrated solutions for the MSW management. Among the solutions adaptable to the context of Beira, one of the many actions of the LimpaMOS project is the construction of a Compost- ing Centre (CeCom). It continues to be carried out by the two technical and scientific main partners (University of Trento and Fondazione Edmund Mach).

Accurate knowledge of the amount and type of MSW produced is one of the basic informa- tion for MSW management. The creation of an updated database contributes substantially to define services and investments needed for collection, transport, form of treatment and final disposal of MSW. At the same time, it contributes to the formulation of strategies for the valorisation of certain fractions, such as the organic one.

The campaign of the MSW analysis made with the technical support to the Department of Urban Management, Equipment and Environment of the Municipality of Beira and was carried out during a period of 5 months, between August and December 2016. Thanks to this analysis, it was possible to elaborate the Municipal Solid Waste Integrated Management Plan of the City of Beira, a fundamental report on the composition of MSW, the current waste management and its future developments. Thirty analyses were carried out in two shifts，

throughout the city. MSW from road containers was analysed, as well as that collected from households living in the so-called informal part of the city, which is characterised by very precarious public or private structures and infrastructures (e.g., areas with houses built with mud and metal sheets and with pedestrian access only). In line with the literature on the com- position of MSW in a low-income context, the OFMSW is the predominant one also for the considered case-study as reported in Figure 1.

The large amount of organic matter present (more than a third of the total composition) leads to the choice of a biological treatment method for its management: one of the most popular treatments, due to its simplicity of management, is the composting process. Collec- tion of the OFMSW at household level is not yet achievable in Beira because of the great material and management criticalities of the MSW collection and transport system. However, in addition to market activities, restaurants play an important role, as they are significant sources of OFMSW production.

In low-income contexts, most MSW is produced by market activities: 35 markets are across the city. These, between formal and informal, differ according to the nature of the products sold and are distinguished by their size and character. The amount of waste material produced in the markets has a strong impact on the collection and final disposal system. There are 16 major markets (MSW output above 100 m3/month). Of these, half produce almost exclusively organic waste while only three produce mixed waste, half of which is organic. In Table 1 some data from five food markets are reported.

To obtain the most realistic projection of the monthly production of MSW from the urban markets, the containers belonging to the markets were identified and it was monitored how many times per week (or per day, as for Maquinino Market) they were emptied by municipal vehicles. Each container has a capacity of 6 m³, so, considering that emptying takes place only once it is full, the volume produced during a working month (28 days) was estimated. The density (0.49 t/m³) assumed for the calculations of the MSW production is the maximum found in the product analysis carried out on containers from the Macurungo district that have the highest organic matter content.

The Maquinino market is the one with the highest production of MSW. Maquinino was chosen as a pilot market to be used to obtain the OFMSW needed for the start-up of the composting centre CeCom. First, it has been subject to a requalification in order to improve:

1. internal waste management through the insertion of small containers inside the market, which can be easily emptied;

2. the internal collection and transport with wheelbarrows;

3. external storage through separate collection in 6 m³ road containers, placed on a new concrete platform adjacent to one of the market’s perimeter walls on which drawings and writing have been made to identify the container for the OFMSW on one side and the one for the inorganic fraction on the other one.

The area where the CeCom will be built is about 1.5 ha and is located in Munhava district. This position was identified using essentially two basic criteria: its proximity to the city’s main landfill site and the existence of a viability to allow access for trucks. CeCom’s Prelimi- nary Project was drafted in 2019 and is not yet in the implementation phase. The plant will provide two different areas for biological treatment:

• ACT (Active Composting Time) area: the bioxidation takes place in covered biocells made of concrete to allow easy loading/unloading operations by a tractor equipped with a shov- el. This area is equipped with an air insufflation system and is kept constantly depressed by a suction system to minimise the olfactory impact of the accelerated phase. The process lasts 28 days in total.

• Maturation zone: here the humification processes take place, and turning operations are implemented. The area is larger than the first phase because the process takes longer (50 days).

The design of the plant is modular, based on an initial small-scale plant that can be expanded in the future to treat a larger quantity of MSW, depending on local demand. Despite the large amount of MSW and OFMSW that can be obtained from the Maquinino market, CeCom was sized considering an input quantity of 1,500 t/year, due to its being the first pilot project for the city. It has been assumed that, in addition to the flow of material from the market, the sur- plus generated by the screening process after maturation can be reused as an internal flow. In this way, the input matrix was considered to be 1,744 t/y. In Table 2 data regarding quantities that could be treated in the CeCom are reported.

The preliminary plant dimensioning foresees the implementation of four 50 m3 biocells for the accelerated bioxidation process. The biocells are closed reinforced concrete structures equipped with a roofing system. The four reactors are connected to a common 6.5 m wide corridor to facilitate the access (via two entrances) and the handling of the heaps. Forced ventilation is provided by the implementation of biomodules or perforated tubes disposed longitudinally. The maturation area has a surface of 1,477.53 m² in which the material is arranged in eight piles 16.5 m long. These are arranged horizontally, side by side, with a 3.3 m distance between each pile. A 10 m manoeuvring space was also considered.

In order to have more information it was decided to analyse the contribution in terms of potential organic matter production of Goto market, the second biggest in the city. The food waste is dumped entirely on the ground and accumulated in open areas next to the stalls. The waste containers were removed because of the accumulation of waste around them, which created unfavourable and even obstructive conditions for the collec- tion vehicles.

The largest areas of accumulation are located inside the market in the western area. In this area, in particular, the uncontrolled dumping of waste (mainly OFMSW), together with poor accessibility and the lack of adequate vehicles for removal, has led to the creation of an open-air dump, where the accumulation of waste has been going on for more than three years. The same problem can be found in the eastern part of the market, where, right at one of the main entrances to the market, there are large heaps of mainly organic waste. The waste is col- lected using a combination of a tractor and a trailer two to three times a week. The waste can remain on the ground for more than a day, spilling out in putrescible and naturally degraded conditions, forming stagnations on the ground, and generating malodorous emissions. In the south-eastern part of the Goto market, near where the removal of the heap of organic matter occurs, there is a large area dedicated only to the delivery of residues from the processing and pressing of sugar cane. Bagasse (the fibrous part and bark of the cane) is produced in the first cycle of pressing and crushing. This slowly biodegradable residue could ideally be used in the composting process as a bulking agent.

Using a questionnaire, the organic waste collection methods of the 15 most popular res- taurants in the city were investigated. By determining the number of containers used in each restaurant, their volume, and the frequency of emptying, it was possible to estimate the poten- tial amount of OFMSW produced annually. For the estimation, it was considered that the per- centage of OFMSW would be 90% if there is separation of the organic fractions. The week was assumed at six working days. Results are shown in Table 3.

The implementation of an organised collection of restaurant waste would involve several logistical and administrative difficulties. First, it would be necessary to guarantee the tem- porary storage of the waste in dedicated containers with an ideal capacity of 120 l located close to the restaurants, which is an economic expense. In addition to temporary storage, as the material is putrescible, adequate removal frequency should be ensured. Second, another critical aspect of this system is the contamination of the waste. The OFMSW that some res- taurants already separate could be disposed of in dedicated external containers for restaurants only. However, it is possible that the inhabitants of the city centre will also start using the restaurants’ containers to deposit their waste.

Every day, the harbour canteen offers a lunch service (11:30h-14:00h) to workers, with up to 200 covers (this data refers to the situation before the COVID-19 pandemic). The involve- ment of the canteen in the compost production chain will give advantages. The port area is located close to the CeCom site and is characterised by good accessibility and roads. In addi- tion to this, the canteen is located outside the city centre and the perimeter of the port area is fenced off and access guarded, so that only workers and citizens who want to use the canteen service have access. The containers, already present within the port area to serve only the canteen, are not used for the delivery of domestic MSW. A purer organic fraction could then be obtained, which would be an optimal matrix for the composting process, and there is also the economic advantage of not having to purchase containers.

Despite Maquinino and Goto markets are considered food markets and therefore have an almost total production of organic matter, this fraction is about 85% of the total MSW in the case of the Maquinino and 95% in the case of the Goto.

The new amount of OFMSW is almost ten times higher than the one considered in the pre- liminary project, increasing from 1,020.24 to 10,062.42 t/year. This requires the calculation of the new CeCom layout, which will be expanded in terms of biocells and maturation area. For the calculation of the total input matrix, two scenarios were considered, depending on the availability of sludge. This is not a strict requirement. It might not even be included in the initial matrix, thus implementing a composting process (instead of co-composting). However, the ability to also treat another problematic fraction such as sludge was considered an important requirement for the design of the CeCom. A higher amount of organic matter corresponds to a higher amount of structuring material and sludge. The incoming sludge to CeCom could be treated biologically at the ETAR water treatment plant, located in the Munhava - Matope district close to CeCom.

Depending on the availability of sludge from ETAR plant, two scenarios can be considered:

• the first scenario refers to a hypothetical availability of sludge equal to 10% of the organic material (thus higher than the quantity foreseen in the preliminary design),

• the second scenario uses the same tonnes on an annual scale as initially assumed in the preliminary project.

In Table 4 the quantities assumed for the two proposed scenarios are reported.

Given the volumes to be treated, the geometry of each biocell, and the number of days required for maturation and discharge operations, it was possible to determine the new number of cells, which is 39 (very small biocells: 5 × 5 m; height: 2 m). More data are reported in Table 5. Maintaining these dimensions (the preliminary project), it can be said that is unrealistic considering the limited availability of means and resources necessary for the construction of the biocells, leading to an increase in costs due to the necessity of equip- ping each biocell with a blower and relative aeration system, as well as logistical difficulties (e.g., the transfer of material to all the biocells leads to an increase in the traffic of vehicles for loading and unloading operations).

It was therefore considered to build seven biotunnels, maintaining the width of 5 m but with a length of 25 m. Biotunnels are easier to construct due to the smaller number of reac- tors. These, together with the initial four biocells capable of treating the preliminary design quantity of 1,744 t/year, will increase the plant’s treatment capacity.

The expansion of the input matrix also entails an expansion of the maturation area for the output material. Table 6 shows the assumptions made for the design of this area, where 24 rows of 25 × 6m will be arranged. Their configuration is the same as in the preliminary pro- ject: heaps are placed side by side two by two for a total of eight heaps per column.

CeCom is a pilot project and new biocells or biotunnels could be built gradually over time. The advantage of having a modular plant means that expansion can be considered in several distinct phases, maintaining the size of the initial cells, and evaluating through subsequent studies the feasibility of building further biocells and/or biotunnels, also depending on the quality of the compost produced.

The extension of the quantities of OFMSW removed from the urban context and its proper management is fundamental for the city of Beira. In addition to the increased production of compost obtainable from the CeCom and the improvement of the hygienic conditions of the urban context, this implementation could bring other benefits.

Beira dump has a surface area of about 20 ha and is currently the only alternative for final waste deposition. MSW dumped does not receive any pre-treatment and is therefore not stabi- lised. Due to the high percentage of organic matter in the waste, biological degradation reactions of the putrescible fraction take place in the dump body, resulting in the production of biogas.

Tas and Belon [41] reported that, in 2014 in Mozambique emissions from uncontrolled landfills reached 76,546 t of carbon dioxide equivalent (CO2-eq) and, if current conditions remained the same, this value would amount to 1,369,721 t in 2030 [31]. The anaerobic deg- radation of one tonne of wet MSW (60% organic matter, 40% moisture) could theoretically generate up to 200 Nm3 of methane. However, a production of approximately 50 Nm3 of methane per tonne of dumped MSW is considered a conservative estimate [38]. Considering a Global Warming Potential factor for methane of 28, the potential amount of CO2-eq that will be removed from atmosphere thanks to the CeCom was estimated and is reported in Table 7: the first row of the table shows the reduction due to the start-up of the CeCom (pre- liminary project), while the second row shows the reduction due to the subsequent expansion of the input matrix.

In low-income contexts, such as Mozambique, waste is not always managed entirely by the municipality or by a public-private partnership. Especially in urban contexts, there is a large proportion of informal workers who contribute significantly to the management of MSW, despite not being regularly paid or subject to a contract. The informal recycling sector of some materials is based on the activities carried out by waste pickers, the so-called catadores, who manually separate some recyclable materials (PET, PP, HDPE and aluminium) from the mixed waste to sell them. Their earnings are based exclusively on the quantities of material brought to the collection point, where the selling price per kg is very low (7 MT for a kg of PET and 4 MT for a kg of aluminium, which are approximately equivalent to 10 eurocents and 6 eurocents). One of the most attractive workplaces for catadores in Beira is the city’s dump, near which there is a collection point for recyclable materials. Many independent workers, families or small organised groups are permanently present at the dump. In addition to the precariousness of their earnings, their health and safety protections at the workplace are almost inexistant.

Until separation of the organic fraction is established, CeCom will need to pre-treat the input matrix by manual sorting to remove residual fractions. This process could be implemented through the work of the catadores, who would then be regularised, trained and paid regularly, allowing them to work in a safe and controlled environment. The quality of compost obtained will be assessed in test fields, refining management practice over time. The first objective is to obtain a soil conditioner with good characteristics that can be used in agriculture.

In all cases, because of the primary need to bio-stabilise the MSW, it is advisable to con- sider the implementation of alternative treatment plants to CeCom that can produce a suitable material for landfill or energy recovery. Biodrying and biostabilisation are potentially appli- cable technologies for this purpose [42-44]. It is important to note that these are proposals for forms of treatment whose output has smaller margins of applicability than composting.

Further evaluations of these technologies must always be made considering the context of the city of Beira. In fact, the biodried material requires a facility suitable for its use (e.g., cement works) and cannot be stored in landfills due to the high concentration of volatile solids in it. Stabilised material, on the other hand, can be safely landfilled but the process is more complex to control (water must be added during treatment) and costs are different.

Training and support for public institutions, municipal or private companies for the man- agement of MSW, and for all citizens are aspects that must necessarily accompany project proposals to improve the entire waste management chain. In Beira there is a requirement that all non-domestic MSW producers (such as restaurant owners) must ensure that their waste is managed by transporting it in their own vehicles or those of the Beira City Council (e.g., by signing a contract that ensures daily service). However, this is not happening regularly, contributing to an increase in the amount of waste deposited in containers for public domestic collection.

Starting a collection of the organic fractions with the markets is a good prospect, both because of the great abundance of it and because of the existence of a collection and trans- port system which, although it has many criticalities, has been operating for years and can be more easily upgraded. Efficiency requires money, which in the future could also come from the sale of good quality compost.