Techno-Economic Performance Assessment of Malt Dust Derived Biochar Application for Municipal Wastewater Treatment: A Water Reuse Strategy ^†

Abstract

Wastewater is a sustainable water supply which uses reclamation and reuse processes to protect freshwater resources. Biochar application is considered an efficient and low-cost wastewater reclamation and reuse technique in recent years. From this perspective, this paper mainly aimed to obtain reclaimed water using biochar application, with an aim of contributing to a circular economy. The major aim of this study was to assess the quality and reuse potential of treated water through the biochar adsorption process. The assessment was based on the EU (741/2020) wastewater reuse legislation. Turbidity, Biological Oxygen Demand (BOD₅), Total Suspended Solid (TSS), and E. coli analyses were performed to determine the effluent quality. In the end of the biochar adsorption process, a Class B reclaimed water quality according to EU legislation was obtained. This study validated that malt-dust-derived biochar is an efficient and low-cost adsorbent and can achieve a high quality of reclaimed water. An average reduction of 31.3% in operational costs was reported compared to an activated sludge system.

1. Introduction

The European Union (EU) Blue Deal has handled the protection and remediation of vulnerable freshwater resources and coped with the water shortages [1]. Wastewater is a sustainable water resource for the freshwater crisis [1,2,3,4]. Reclaimed water plays a crucial role in the water cycle since it constitutes an effective way to improve the utilization of water resources and can help to cope with the water crisis [1,2,3]. Specifically, wastewater reuse can be used as reclaimed water for crop and plant irrigation [1,2,3,4]. Effective wastewater treatment techniques should be applied to achieve the desired reclaimed water quality according to the EU (741/2020) legislation [5]. In recent years, biochar adsorption has been regarded as an effective and low-cost wastewater treatment technology [6,7,8,9,10]. Most biochar adsorption effluents comply with regulatory standards for reuse scenarios in urban and agricultural aims [6,7,8,9,10]. Biochar could easily adsorb the recalcitrant organic and solid materials and pathogens into the body [6,7,8,9,10]. Reclaimed water should contain a lower concentration of organic solid materials and minimum microorganisms. Biochar application is an efficient removal technique for these undesirable pollutant parameters [6,7,8,9,10].

Waste reduction and recycling are two of the main strategies which have favorable effects in terms of a circular economy, and they are one of several environmental remedies included in the European Union’s (EU) Green Deal aims [11,12,13,14]. Malt dust, which is an agro-industrial waste in larger amounts, was used for the biochar production, so waste reduction was indirectly ensured. This study is novel in that malt dust derived biochar was used for wastewater treatment to achieve the reclaimed water. In the literature, there is a limited point of view related to water reuse applications in terms of biochar application. Cosenza et al. (2024) used a membrane bioreactor to achieve the reclaimed water from municipal campus wastewater (Cosenza et al. 2024) [2]. Quispe et al. (2023) investigated the optimization of biochar filter for handwashing wastewater treatment and potential treated water reuse for handwashing [4].

The main theme of this paper was that the investigation of irrigation potential of reclaimed water using biochar. The major aim of this study was to evaluate the quality and reuse potential of treated effluent by the biochar adsorption process. This paper also aimed to obtain reclaimed water using biochar application, with an aim of contributing to a circular economy. The assessment was based on EU (741/2020) wastewater reuse legislation. According to the legislation, pH, total suspended solids (TSS), biological oxygen demand (BOD₅), turbidity, and Escherichia coli (E. coli) are the restricted parameters in reclaimed water needed to meet the minimum water quality criteria [5]. From this point of view, these parameters were considered for evaluation in this study. Biochar application in wastewater treatment produces high quality effluents [11,12]. Specifically, heavy metal, organic materials [15,16,17,18,19,20], and pathogen [21,22,23] removal efficiencies from different wastewater reached up to 90–97% using biochar derived from various feedstocks in the literature. In the literature, membrane processes were generally applied to achieve the reclaimed water quality. There are many advantages of biochar application as a wastewater reuse and reclamation techniques [4]. While comparing with other treatment techniques such as membrane processes, biochar application is a low-cost and efficient water reuse and reclamation technique. There are no higher energy requirements for operating, or freshwater depletion for cleaning. From this point of view, biochar application is a promising technology with positive effects on the circular economy. Biochar application is also considered as a waste reduction technique owing to the use of biowastes as feedstock. In terms of the circular economy perspective, waste biochar (waste adsorbent) could be used as a soil conditioner or manure, with an agricultural use, after several analyses. Waste biochar could also be regenerated by re-pyrolyzing it to produce fresh adsorbents. As a sustainable approach, waste biochar could be used as a new feedstock for biochar. This approach offers dual benefits: reducing industrial waste and contributing to environmental protection; providing a sustainable, cost-effective solution for wastewater treatment, particularly in resource-limited areas.

2. Materials and Method

The overview of the system and conceptual framework of the research is given in Figure 1. The experimental procedure in this study was based on water analyses. The benchmarking was performed with a conventional activated sludge system instead of biochar application. A techno-economic assessment was performed based on these two systems. The operational costs included water consumption (freshwater consumption for green area irrigation on the campus instead of reclaimed water use) and energy consumption (energy requirement for the aeration process). The influent and effluent analyses were performed (TSS, BOD₅, pH) according to the standard methods [24]. Turbidity and E. coli analyses were performed by a certified laboratory.

The influent of the adsorption process was the municipal wastewater from campus kitchen sink. The influent characteristics were given in

Table 1. Raw wastewater characteristics.

Parameter	Value
TSS (mg/L)	221
Turbidity (NTU)	33
BOD5 (mg/L)	415
E. coli (Cfu/100 mL)	55

. It is a greywater which could be treated efficiently by biochar.

Biochar was produced using malt dust which was obtained from a brewery industry in Turkey. A fluidized bed reactor was used for slow pyrolysis at 250, 300, and 500 °C (M1, M2 and M3), respectively. X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectrometry (FTIR), and BET (Brunauer, Emmett, and Teller) analyses were applied to define the characterization and the major properties of the biochar.

This study was based on wastewater analyses and the biochar adsorption process. Wastewater samples were taken seasonally. Similarly, the adsorption process was performed seasonally. Pathogen (E. coli) adsorption onto the biochar was investigated. An adsorption column with a volume of 1 L was used. The mixture of three types of biochar was added in the amount of 12 g, in total. In this study, a new pollutant adsorption calculation model was developed based on general adsorption theory by Metcalf and Eddy (2014) (Equation (1)) [25].

$$\mathrm{qe}={\displaystyle \frac{(\mathrm{P}\mathrm{i}-\mathrm{P}\mathrm{e})\mathrm{W}}{\mathrm{B}}},$$

(1)

where

Pi: Influent concentration (mM)

Pe: Effluent concentration (mM) (after biochar adsorption)

W: Wastewater volume (L)

B: Biochar dose (g)

qe: The quantity of pollutants onto the biochar (mmol/g)

3. Results and Discussion

The results revealed that malt dust-derived biochar is an efficient and low-cost technology to achieve reclaimed water. According to the overall assessment, the effluent related to biochar adsorption process met the requirements for Class B quality reclaimed water.

Table 2. Effluent characteristics for water reuse.

Parameter	Winter	Spring	Summer	Autumn	Class A	Class B
TSS (mg/L)	3	7.5	8	5	≤10	≤35
Turbidity (NTU)	4.5	8	9.5	6	≤5	_
BOD5 (mg/L)	10	13	15	11.5	≤10	≤25
E. coli (Cfu/100 mL)	0.25	1.25	2.5	0.75	≤10	≤100

showed the average effluent characterization for water reuse after biochar adsorption process and minimum reclaimed water quality criteria for Class A and Class B waters. As seen from Table 2, E. coli values met the Class A quality for each season. TSS for all seasons and turbidity and BOD₅ in winter met the Class A quality when the others met the Class B quality. According to the overall assessment, the effluent met the requirements for the Class B reclaimed water quality. Class A quality reclaimed water can be used for all types of crops (root crops, above low-ground crops, and high-ground crops) consumed raw. On the other hand, Class B quality reclaimed water is suitable for above low-ground and high-ground crops. In this study, the reclaimed water was used for the grass irrigation. In the literature, there was a restricted point of view related to this topic. In general, membrane processes were applied [2]. Cosenza et al. (2024) similarly reported Class B reclaimed water using a membrane bioreactor [2]. Quispe et al. (2023) reported the optimization of biochar filter for handwashing wastewater treatment and potential treated water reuse for handwashing [4].

As comparing energy and water consumption for two scenarios which were with and without reuse, the operational cost was higher without reuse. If water reuse and biochar was used, approximately 31.3% of reduction on operational costs was reported (Figure 2). This study showed that biochar was a cost-effective and low-cost application.

In this study, pathogen adsorption onto the malt dust derived was investigated.

Table 3. Results of E. coli adsorption.

		Adsorbents
E. coli adsorption	M1	M2	M3
qe (mmol/g)	9.41	9.00	8.93

showed the adsorption results in detail. According to the adsorption results, the most effective biochar was M1, which was produced at the lowest temperature.

4. Conclusions

This study showed that malt dust-derived biochar could not only adsorb the pollutants from wastewater but also ensure the quality of reclaimed water. By the end of the treatment, the reclaimed water obtained met the requirements of the Class B water according to European Union (EU) (741/2020) legislation. Approximately, a 31.3% reduction in operational costs was achieved using biochar adsorption, compared to conventional activated sludge system.