Insights on Harnessing Domestic Biowaste for Greening the Green City of Benguerir in Morocco

Abstract

As the human population grows, the amount of household-generated waste is projected to grow. However, data on the amounts of household-generated waste are lacking in many regions. Uncertainties in the amounts and fractions of biowaste make it challenging to manage actions that reduce its environmental impacts and generate value. The current observational study sought to quantify and characterize the household waste generated in the green city of Benguerir. To achieve this objective, we surveyed waste generation rates in 68 randomly selected households. The results showed that, on average, 0.69 kg of waste was generated per person per day. An average of 80% of the household-generated waste was biowaste, which, if managed appropriately, represents a valuable source of plant nutrients. We estimated that shifting from the current landfill disposal of biowaste to its utilization for compost and biogas production will result in up to an 88% reduction in greenhouse gas emissions. These findings suggest that managing household waste will be vital for reducing city-wide carbon emissions and simultaneously creating employment in the waste management sector.

1. Introduction

Household waste represents a combination of disposable hazardous and non-hazardous material generated at the household level [1]. However, an accurate understanding of household-level waste generation and its management is compromised by data unavailability and lack of access to available data [2]. Moreover, most of the available household waste data are based on theoretical estimation rather than actual measurements [3,4,5]. In Morocco, the amount of domestic solid waste generated daily ranges between 0.3 and 0.76 kg per capita in rural and large urban households, respectively [6]. However, data on the composition and characteristics of the generated household waste, especially the organic part, is lacking, thus creating a barrier in selecting economically feasible and socio-culturally appropriate approaches to manage and treat the waste. Despite the lack of data on the amounts of waste generated at the household level, poor waste management negatively affects the environment [3]. In this exploratory observational study, we sought to quantify and characterize the amounts of biowaste generated by households in the green city of Benguerir. The generated data were used to estimate greenhouse gas emissions linked to waste dumping compared to those from two other waste management options: composting and anaerobic digestion.

2. Materials and Methods

2.1. Observational Study Area

The observational study was conducted in the green city of Benguerir (32°14′34.82″ N, 7°57′34.54″ W) in central Morocco. According to the last census (2014), the number of inhabitants in Benguerir was 88,624 [7]. However, currently, the estimated population is 111,331 inhabitants [8]: the population statistic we used in this observational study.

2.2. Household Waste Quantification

From 22 February to 22 April 2022, waste generation rates at the household level were determined by collecting waste generated in 68 randomly selected households for at least seven days. The sampled households had heterogeneous income levels. However, data on income levels were not collected to avoid private and sensitive information. The method described by Salant and Dillmann [9] and Rea and Parker [10] was used to determine that the 68 households resulted in a sampling error of ±12%.

Each participant was given plastic bags to dispose of all waste generated in the different households. On each sampling day, plastic bags were collected, and the weight and number of people in the household were recorded. The amounts of waste generated during the sampling period and the number of people in the different households enabled us to calculate the average per capita waste generation rates (kg per person per day). The amounts of domestic waste generated in Benguerir were then estimated by multiplying the average per capita waste generation rates by the number of habitats (111,331). The waste composition was determined by emptying all the bags collected on the same day on a flat, covered surface. The waste was mixed and then sorted into different waste fractions (i.e., biowaste, paper and cardboard, plastic, textiles, metals, glass, and others) and weighed. The weight of each waste fraction divided by the total waste collected during the week estimates the proportion of the different waste fractions [11].

2.3. Marco-Nutrient Quantification in Household Waste

For the biowaste, well-homogenized samples collected on four sampling days were weighed, oven dried for 48 h at 60 °C, and weighed again for moisture content determination.

The total nitrogen content of the studied samples was determined according to the official methods of analysis of AOAC International (Association of Official Analytical Chemists) using a Kjeltec 2300 autoanalyzer (Hilleroed, Denmark). Precisely, 0.3 g of dry organic material was placed in a digestion tube with 10 mL of sulfuric salicylic acid (30:1 vw) mixture. The tubes were then placed in a Kjeldahl catalyst and heated to 380 °C for 2 h until the samples turned hyaline. Finally, total nitrogen was determined by distillation.

For phosphorus and potassium content, 500 mg of dry matter was weighed and placed in a digestion tube for mineralization, and then 7.5 mL of HNO₃ 65% was added. The tubes remained open for 20 min to avoid a process interruption due to a rapid increase in pressure. They were then closed, positioned inside the microwave rotor, and digested for two hours at 90 °C. The final volume was adjusted to 50 mL with deionized water. The final solution was quantitatively transferred to a polypropylene tube and filled up to 10 mL. Multi-elemental trace analysis of previously digested samples was carried out using the Agilent 5110 ICP-OES (Santa Clara, CA, USA).

2.4. Greenhouse Gas Emissions Estimation

Greenhouse gas emissions were estimated using the method described by Kristanto and Koven [12] and Manfredi et al. [13]. Precisely, greenhouse gas emissions from waste treatment were calculated using the equation

Emission = EF × m

where m is the mass of biowaste (tons) and EF is the emission factor (kg of GHG/ton). The emissions factors for the different waste management methods are given in

Table 1. Emission factors for waste management approaches.

Management System	Greenhouse Gas	EF	Unit	Reference
Landfill dumping	CH4	1000	kg CO2-eq/ton wet biowaste	[13]
Anaerobic digestion	CH4	125	kg CO2-eq/ton wet biowaste	[14]
Composting	CH4	100	kg CO2-eq/ton wet biowaste	[14]
	N2O	71.52	kg CO2-eq/ton wet biowaste	[14]

.

3. Results

3.1. Waste Generation

The average amount of waste generated was 0.69 kg per person per day (0.59–0.80 kg per person—Confidence Interval (CI) 95%). For the 111,331 inhabitants of Benguerir, this translates to 76,818 kg (65,685–89,065 kg CI 95%) of daily waste. Since an average of 80% of the generated waste was organic material, we estimated that about 61,454 kg (52,548–71,252 kg CI 95%) of the daily waste was biowaste.

3.2. Organic Waste Characterization

The results on the macro-element composition of the organic waste generated in the city of Benguerir are provided in

Table 2. Nitrogen (N), phosphorous (P), and potassium (K) contents of the organic fraction of biowaste generated by households in Benguerir on four sampling days.

Element	Average (%)	Coefficient of Variation	Standard Deviation
N	2.67	36%	0.96
P	0.57	45%	0.26
K	1.57	33%	0.52

.

Using the results in Table 2 and an average measured moisture content of 80%, we estimated that N, P, and K contents in city-wide generated biowaste are correspondingly about 326, 70, and 192 kg per day.

3.3. GHG Emissions

Using the emission factors included in Table 1, GHG emissions from municipal biowaste in different management systems are given in

Table 3. GHG emissions from different waste management approaches.

Management System	Greenhouse Gas	Tons of CO2-eq per Day
Landfill dumping	CH4	61.45
Anaerobic digestion	CH4	7.68
Composting	CH4	6.15
	N2O	4.40

.

Table 3 shows that the current biowaste treatment emits 6 to 8 times CO₂-eq compared to anaerobic digestion and composting.

4. Discussion

The waste generation rates (0.69 kg per person per day; 0.59–0.80 kg per person CI 95%) observed in this study corroborated with estimates from other studies (0.76 kg per capita per day) conducted in urban areas in Morocco [6,15]. Similarly, the high proportion of biowaste, which represents an untapped biomass resource, was also reported by other studies conducted in other developing countries [16,17,18,19]. Consequently, the similarity of household waste generation levels and the proportion of biowaste observed in our study with those cited in this study suggests a possibility to extrapolate our findings and recommendations to other cities in Morocco and other developing countries. Furthermore, the biowaste can be harnessed to provide value at the household or city level by adopting several waste utilization options, such as diverting organic waste from landfills to composts or biogas plants. Compared to current waste management systems such as landfill dumping, which result in high GHG emissions (61.45 t CO₂-eq per day), the adoption of improved waste management practices (i.e., anaerobic digestion and composting) can result in up to an 88% reduction in GHG emissions or the avoidance of 19.63 Gg of CO₂-eq per year.

The daily macronutrient contents in generated biowaste can support agricultural production and thus reduce mineral fertilizer inputs required to support crop production. Assuming biowaste production remains at the same level throughout the year, an estimated 119, 25, and 70 tons of N, P, and K, respectively, could be available to support agricultural production. To utilize these nutrients, composted or vermicomposted biomass and the digestate from anaerobic digestion can be applied as a soil amendment in future urban agriculture initiatives and mine soil rehabilitation projects to support agricultural production and land rehabilitation actions in the area.

The projected increase in human population is expected to increase biowaste production, and if no improved waste management measures (i.e., composting or anaerobic digestion) are adopted, an increase in wasted-related greenhouse gas emissions and nutrient losses can be expected. Current projections suggest that Benguerir’s population will increase to 135,506 by 2030 [8], which, using the waste generation rates we observed, will increase waste production by 22%. Therefore, to support the low-carbon ambitions of the green city of Benguerir, local authorities urgently need to consider investing in low GHG-emitting waste management options.

These findings suggest that adopting improved waste management actions presents an enormous opportunity to utilize biowaste as a soil amendment (Table 2) and reduce biowaste-related carbon emissions, which should simultaneously create employment in the waste management sector. In addition, biowaste valorization can help to alleviate municipal expenditure through the reduction of the volume of waste going to landfill, recovery of waste management costs through revenue from the selling of the organic amendment and biogas, and avoiding leachate management costs originating from the organic solid waste which constitutes a threat to public health.

Morocco has made significant efforts, starting with law No. 28-00 on waste management in 2006, adopting the National Household Waste Programme in 2008, and developing the National Sustainable Development Strategy in 2017. However, these efforts are still insufficient, and to achieve the intended outcomes, more policy innovations and actions are needed to raise awareness and increase the visibility of and level of investment in opportunities linked to improved waste management. We propose that national or sub-national policies should focus on incentivizing investments in key infrastructure, technologies, and processes that support waste separation and management at both the household and city scales.