Realistic and field scale applications of biochar for water remediation: A literature review

Biochar has received increasing attention in recent years as a potentially cost-competitive adsorbent for removing various contaminants from surface water and groundwater. However, most published studies have been conducted in the laboratory on a bench scale. Laboratory conditions do not necessarily reflect the complex, heterogeneous, and dynamic field conditions of actual contaminated surface water and groundwater environments. There is a lack of comprehensive literature review regarding the performance of biochar for contaminant removal, especially under realistic field conditions and at field scale. Here, we evaluated 31 studies on realistic applications of biochar for water remediation by searching the keywords: pilot scale, field scale, and mesocosm scale combined with biochar and water remediation. Biochar was found to be incorporated into a variety of water remediation technologies for treating both inorganic and organic contaminants, such as nutrients, heavy metals, pesticides, and pharmaceuticals in polluted waters and wastewaters. Also, biochar showed the potential to be effective on a field scale or in realistic remediation technologies, although it is not always as effective as other sorbents, such as activated carbon (AC). This is partially because AC has better physicochemical characteristics such as higher surface area and more micropores. Effectiveness for contaminant removal varies according to the targeted contaminants, the type and dosage of biochar used, and the treatment technology incorporating biochar. Finally, knowledge gaps and future research areas are identified. For example, more field scale studies are needed to test the effectiveness of biochar as an adsorbent under realistic conditions to pinpoint specific characteristics suitable for target contaminants. Physicochemical characteristics of the biochar can also change over time during the treatment process due to weathering, which may negatively affect the treatment performance. The effects of scaling up production on biochar quality should therefore also be further investigated, as physicochemical characteristics can be affected by varying the synthesis conditions. Regeneration and disposal of spent biochar is another active research area to determine the overall treatment costs.

Greywater reuse for irrigation: A critical review of suitability, treatment, and risks

Greywater accounts for approximately 75 % of domestic wastewater and generally contains fewer contaminants than domestic wastewater. Therefore, its treatment and reuse represent a promising approach to supplement irrigation demand. This study comprehensively evaluates the quality characteristics of greywater based on its source, applied treatment methods, and its potential health, environmental, soil, and agricultural impacts. Various physical, chemical, and biological treatment processes have been analysed, with the most commonly employed technologies including membrane bioreactors (MBRs), constructed wetlands, media filtration (sand, activated carbon), disinfection methods (UV, chlorine, ozone), and advanced oxidation processes. The effectiveness of these methods has been assessed concerning the intended reuse application, emphasizing the critical role of disinfection in ensuring safe irrigation use. The health and environmental implications of greywater reuse have been examined, focusing on the risks associated with pathogen contamination, detergent residues, and micropollutants, while also evaluating the efficiency of treatment processes in mitigating these risks. From an environmental perspective, the accumulation of essential nutrients such as nitrogen and phosphorus, the potential for salinity buildup, and alterations in soil microbial balance have been investigated. Regarding soil and agricultural impacts, this study analyzes how greywater reuse influences soil structure (e.g., permeability, infiltration), plant growth responses, and the accumulation of heavy metals. These findings contribute to the development of scientifically grounded recommendations for the safe and sustainable reuse of greywater within water management strategies, promoting its role as an alternative water source for irrigation.

Treated greywater as a novel water resource: The perspective of greywater treatment for reuse from a bibliometric analysis

The current global water crisis has prompted research into technologies that can reuse different water resources to mitigate water scarcity. The use of treated greywater can be proposed to provide additional water resources. By reusing this water in different applications, this water crisis can be mitigated at the local scale. This study presents a bibliometric analysis to assess the state of the art of greywater treatment and its reuse technologies. This analysis is based on the scientific literature published until 2023 in Scopus regarding greywater treatment and 1,024 documents were found. The results showed a clear exponential increase in the accumulated number of publications in this topic, which was spurred during the mid-1990s. The most prolific country was the United States, while China, the other typical scientific superpower in most fields, occupied the sixth position in the ranking. Environmental Sciences was the knowledge subject with more documents, followed by Engineering and Chemical Engineering. The bibliometric study was complemented using SciMAT to create bibliometric networks that represent the dynamic evolution of the themes. The most important themes were identified, among which three key points stand out: greywater characterization, technologies for greywater treatment, and water management, including the reuse of treated greywater.

Biochar-based fixed filter columns for water treatment: A comprehensive review

Biochar used in fixed filter columns (BFCs) has garnered significant attention for its capabilities in material immobilization and recovery, filtration mechanisms, and potential for scale-up, surpassing the limitations of batch experiments. This review examines the efficacy of biochar in BFCs, either as the primary filtering material or in combination with other media, across various wastewater treatment scenarios. BFCs show high treatment efficiency, with an average COD removal of 80 % ±15.3 % (95 % confidence interval: 72 %, 86 %). Nutrient removal varies, with nitrogen-ammonium and phosphorus-phosphate removal averaging 71 ± 17.1 % (60 %, 80 %) and 57 % ± 25.6 % (41 %, 74 %), respectively. Pathogen reduction is notable, averaging 2.4 ± 1.12 log10 units (1.9, 2.9). Biochemical characteristics, pollutant concentrations, and operational conditions, including hydraulic loading rate and retention time, are critical to treatment efficiency. The pyrolysis temperature (typically 300 to 800 °C) and duration (1.0 to 4.0 h) influence biochar's specific surface area (SSA), with higher temperatures generally increasing SSA. This review supports the biochar application in wastewater treatment and guides the design and operation of BFCs, bridging laboratory research and field applications. Further investigation is needed into biochar reuse as a fertilizer or energy source, along with research on BFC models under real-world conditions to fully assess their efficacy, service life, and costs for practical implementation.

Life cycle assessment of biochar filters for on-site wastewater treatment

Biochar is a promising filter material for wastewater treatment. This study evaluated the environmental (climate, eutrophication, acidification) impacts of biochar filters for onsite wastewater treatment and compared them with those of a conventional sand filter. Using a parameterised life cycle assessment (LCA) approach, these three impact categories were quantified for two designs of biochar filter and a sand filter, used in normal and sensitive areas as defined by Swedish government recommendations. Different scenarios for the biochar filters, with different combinations of biochar supply chain, biochar end-of-life and energy system, were simulated and analysed. The eutrophication impact of the biochar filters was similar to that of the sand filter, while the acidification impact was generally slightly higher than that of the sand filter in sensitive areas, and lower in normal areas. The climate impact of the biochar filter varied considerably, from substantially higher to lower than that of the sand filter, depending on specific scenario. A few scenarios in which biochar filters had lower overall impacts than the sand filter were identified. In general, the biochar filters had lower environmental impacts in a renewable energy context than in a fossil fuel context. Using biochar in landscaping soil was a better end-of-life alternative than combustion. Biochar from syngas-heated pyrolysis performed considerably better than biochar from electricity-heated pyrolysis in a fossil energy context. Direct emissions to air and water from the wastewater treatment process, production of biochar and biochar end-of-life contributed most to the total impacts and variation in these for all biochar systems.

Greywater treatment in a green wall using different filter materials and hydraulic loading rates

Green walls in urban environments can be both an aesthetic feature and be of practical use in greywater treatment. This study evaluates the effect of different loading rates (4.5 l/d, 9 l/d, and 18 l/d) on the efficiency of treating actual greywater from a city district in a pilot-scale green wall with five different filter materials as substrates (biochar, pumice, hemp fiber, spent coffee grounds (SCG), and composted fiber soil (CFS)). Three cool climate plant species, Carex nigra, Juncus compressus, and Myosotis scorpioides, were chosen for the green wall. The following parameters were evaluated: biological oxygen demand (BOD), fractions of organic carbon, nutrients, indicator bacteria, surfactants, and salt. Three of the five materials investigated - biochar, pumice, and CFS - showed promising treatment efficiencies. The respective overall reduction efficiencies of BOD, total nitrogen (TN) and total phosphorus (TP) were 99%, 75%, and 57% for biochar; 96%, 58%, and 61% for pumice; and 99%, 82% and 85% for CFS. BOD was stable in the biochar filter material with effluent concentrations of 2 mg/l across all investigated loading rates. However, higher loading rates had a significantly negative effect on hemp and pumice for BOD. Interestingly, the highest loading rate (18 l/d) flowing over pumice removed the highest levels of TN (80%) and TP (86%). Biochar was the most effective material in removing indicator bacteria, with a 2.2-4.0 Log₁₀ reduction for E. coli and enterococci. SCG was the least efficient material, giving a higher BOD in the effluent than in the influent. Therefore, this study presents the potential of natural and waste-derived filter materials to treat greywater effectively and the results can contribute to the future development of nature-based greywater treatment and management practices in urban areas.

Greywater reuse: an assessment of the Jordanian experience in rural communities

Water conservation is a critical issue, particularly in arid countries and countries that suffer a lack of natural water resources. Jordan is one of the most water-scarce countries in the world; this fact has forced the search for alternative sustainable solutions. With the support of several regional and international organizations, tens of projects were implemented across the country over the past 30 years that aimed to reuse greywater in rural communities. The current review provides a wide overview of Jordan's experience in greywater treatment and its reuse for non-potable purposes in rural areas. To the best knowledge of the authors, the present review is the first to assess the Jordanian experience in this field. Many governmental authorities and non-governmental organizations have been involved in Jordan's experience. The greywater reuse systems were established to achieve advantageous environmental and socio-economic consequences on the rural communities. The strategy of greywater treatment was based on a local on-site greywater treatment system in households or the so-called 'autonomous water management'. The applied greywater treatment technologies in households were found efficient in rendering greywater adequate for agricultural uses. However, further improvements and territorial expansion of the experiment are needed.

Pilot Tests on the Treatment of Bath Wastewater by a Membrane Bioreactor

In order to save water and reduce the cost of water in public areas, we studied the feasibility of recycling bath wastewater by a membrane bioreactor (MBR) at a college campus scale. The results showed that the treatment of bath wastewater by the MBR could achieve a chemical oxygen demand (COD) <50 mg/L with an average removal rate of 83%, a final NH₃–N concentration of <10 mg/L with an average removal rate of 72%, and a turbidity of <0.5 ntu, with an average value of chromaticity of 26.4 tu. The treated water could meet or exceed the urban miscellaneous water standard of China (GB/T 18920-2002), and the processing cost is 1.70 CNY/m³ or 0.25 USD/m³, which is below the price of tap water. The results demonstrated both the economic benefit and the conservation of natural resources.

Sorption, coagulation, and biodegradation for graywater treatment

Population growth and climate change are exacerbating water scarcity. Graywater recycling could reduce water demand but it is not commonly practiced because of high treatment costs. Biochar, an emerging low-cost alternative sorbent with potential environmental benefits for graywater treatment, was compared to activated carbon (AC) for removing dissolved organic carbon (DOC) from graywater. The impact of pretreatments (coagulation, biodegradation) were also evaluated. Among five biochars tested, a wood-based biochar was the most effective for graywater treatment, but AC removed more DOC. Sorption resulted in a greater percent removal of ultraviolet (UV) absorbance than DOC or free chlorine demand. Graywater regulations could not be met by sorption alone but could be met with pretreatment before sorption. After biodegradation, irrigation and toilet flushing treatment targets could be achieved with AC doses less than 0.7 g/L, while a biochar dose of about 1 g/L was needed to achieve the irrigation treatment targets. For DOC removal, alum coagulation at a dose of 30 mg/L was a less effective pretreatment than biodegradation. Pretreatment and sorption to decrease turbidity and increase UV transmittance could be effective for the potential use of UV disinfection, thus creating an effective graywater non-potable reuse approach.

Quantity and quality characteristics of greywater: A review

Due to depletion of water resources and increased water demand, greywater reuse is gaining popularity as a means of water conservation all over the world. Availability of reliable data on greywater generation and quality characteristics is important in deciding the treatment system and the reuse option. This paper summarises quantity and quality characteristics of greywater reported from different parts of the world. Greywater generation from different countries is compared and its variability is discussed. Important pollutants of concern in greywater such as organic content, nutrients, microorganisms, metals and organic micropollutants from different greywater sources such as bathrooms, hand basins, kitchen and laundry are described. The review shows large variations in greywater quality and quantity with respect to time and source, and the selection of a treatment system would largely depend on this variability. The review also shows that at the levels found in greywater, heavy metals and organic micropollutants in recycled greywater generally do not pose a threat to human health if treated properly.

UV Inactivation of Rotavirus and Tulane Virus Targets Different Components of the Virions

Enteric viruses are shed in fecal material by humans and other animals and are common contaminants in wastewater and surface water. Wastewater treatment plants often disinfect this effluent with low-pressure and medium-pressure UV lamps, which emit 254-nm and 220- to 280-nm irradiation, respectively. It is not known whether this treatment is efficacious against enteric viruses or how such treatments may inactivate these enteric viruses. This study examined UV disinfection for two enteric viruses: rotavirus (RV) (strain OSU with double-stranded RNA and a three-layer capsid) and Tulane virus (TV) (a cultivable surrogate for human norovirus with single-stranded RNA and a single-layer capsid). Viruses were treated with UV irradiation at 220 or 254 nm under conditions relevant to wastewater stabilization ponds, whose water is often used for irrigation. TV was susceptible to 220- or 254-nm UV at similar levels. It appears that UV irradiation inactivated TV by mutagenizing both its genome and capsid binding proteins. RV was more susceptible to UV at 220 nm than to UV at 254 nm. UV irradiation of RV at either 220 or 254 nm resulted in a virus that retained its ability to bind to its host cell receptor. After 220-nm treatment, the VP7 segment of the RV genome could not be amplified by PCR, suggesting that this treatment mutagenized the viral genome. However, this correlation was not observed when UV at 254 nm was used. Thus, RV and TV, with different genome and capsid contents, are targeted by UV irradiation in different ways.IMPORTANCE UV irradiation is becoming common for disinfection in water treatment plants, but little is known about the effectiveness of this treatment for enteric RNA viruses. Here, we observed that 220-nm UV irradiation was efficacious against rotavirus (RV) and Tulane virus (TV). UV irradiation at 254 nm inactivated TV to a greater extent than RV. Additional assays showed that UV irradiation compromised different portions of the RV and TV life cycles. UV irradiation decreased the binding of TV to its host receptor and mutagenized the TV genome. UV irradiation at 220 nm appeared to allow RV-host receptor interaction but halted RV genome replication. These findings provide knowledge about the disinfection of waterborne viruses, information that is important for the safe reuse or release of treated wastewater.

Biochar filters as an on-farm treatment to reduce pathogens when irrigating with wastewater-polluted sources

Microbial contamination of vegetables due to irrigation with wastewater-polluted streams is a common problem around most cities in developing countries because wastewater is an available source of water and nutrients but wastewater treatment is often inadequate. On-farm treatment of polluted water is a feasible option to manage microbial risks in a multi-barrier approach. Current evidence indicates good suitability of biochar filters for microbe removal from wastewater using the hydraulic loading rate (HLR) designed for sand filters, but their suitability has not been tested under on-farm conditions. This study evaluated the combined effect of several variables on removal of microbial indicators from diluted wastewater by biochar filtration on-farm and the correlations between removal efficiency and HLR. Columns of biochar with three different effective particle diameters (d₁₀) were fed with diluted wastewater at 1x, 6x, and 12x the design HLR and two levels of water salinity (electrical conductivity, EC). Influent and effluent samples were collected from the columns and analyzed for bacteriophages (ɸX174 and MS2), Escherichia coli, Enterococcus spp., and Saccharomyces cerevisiae. Microbe removal decreased with increasing HLR, from 2 to 4 to 1 log₁₀ for bacteria and from 2 to 0.8 log₁₀ for viruses, while S. cerevisiae removal was unaffected. Effective particle diameter (d₁₀) was the main variable explaining microbe removal at 6x and 12x, while EC had no effect. Correlation analysis showed removal of 2 log₁₀ bacteria and 1 log₁₀ virus at 3x HLR. Thus biochar filters on-farm would not remove significant amounts of bacteria and viruses. However, the design HLR was found to be conservative. These results, and some technical and management considerations identified, can assist in the development of a scientific method for designing biochar filters for on-farm and conventional wastewater treatment.

Quantitative Microbial Risk Assessment and Infectious Disease Transmission Modeling of Waterborne Enteric Pathogens

PURPOSE OF REVIEW

Waterborne enteric pathogens remain a global health threat. Increasingly, quantitative microbial risk assessment (QMRA) and infectious disease transmission modeling (IDTM) are used to assess waterborne pathogen risks and evaluate mitigation. These modeling efforts, however, have largely been conducted independently for different purposes and in different settings. In this review, we examine the settings where each modeling strategy is employed.

RECENT FINDINGS

QMRA research has focused on food contamination and recreational water in high-income countries (HICs) and drinking water and wastewater in low- and middle-income countries (LMICs). IDTM research has focused on large outbreaks (predominately LMICs) and vaccine-preventable diseases (LMICs and HICs). Human ecology determines the niches that pathogens exploit, leading researchers to focus on different risk assessment research strategies in different settings. To enhance risk modeling, QMRA and IDTM approaches should be integrated to include dynamics of pathogens in the environment and pathogen transmission through populations.

Bacterial community activity and dynamics in the biofilm of an experimental hybrid wetland system treating greywater

The objectives of this study were to determine the biofilm microbial activity and bacterial community structure and successions in greywater treatment filters and to relate the treatment efficiency to the bacterial community parameters. This 10-month study was performed in a newly established experimental system for domestic greywater treatment that consisted of three parallel vertical flow filters (VFs) followed by a horizontal flow filter (HF). A rapid increase in the bacterial community abundance occurred during the first 85 days of filter operations, followed by a short-term decrease and the stabilization of the 16S rRNA gene copy numbers at average levels of 1.2 × 10⁹ and 3.2 × 10⁸ copies/g dw in VFs and HF, respectively, until the end of the experiment. The dominant bacterial phyla and genera differed between the VFs and HF. The temporal variation in the bacterial community structure was primarily related to the species replacement, and it was significantly affected by the influent organic carbon and nitrogen compounds in the VFs and the ammonia and organic carbon in the HF filters. Despite the differences in the community structure and assembly mechanisms, the temporal dynamics of the bacterial community showed high congruence between the filter types. The treatment efficiency was related to the biofilm bacterial community diversity and abundance and the abundance of certain bacterial genera in the VF filters. The results suggest that the dominant pathway of nitrogen removal by greywater treatment VFs occurs via coupled heterotrophic nitrification and denitrification, while the contribution of aerobic denitrification is temporally variable in these filters.

Potential of Biochar Filters for Onsite Wastewater Treatment: Effects of Biochar Type, Physical Properties and Operating Conditions

The potential of biochar as a filter medium for onsite wastewater treatment was investigated in five sub-studies. Sub-study 1 compared pollutant removal from wastewater using pine-spruce biochar, willow biochar and activated biochar (undefined biomass) filters. Sub-study 2 investigated the effects of particle size (0.7, 1.4 and 2.8 mm) on pollutant removal using pine-spruce biochar filters. In sub-studies 3 and 4, the effects of the hydraulic loading rate (HLR; 32–200 L m−2) and organic loading rates (OLR; 5–20 g biochemical oxygen demand (BOD5) m−2) on pollutant removal using pine-spruce biochar filters were investigated, while sub-study 5 compared pollutant removal in pine-spruce biochar filters and in sand. The removal of chemical oxygen demand (COD), total nitrogen (Tot-N), ammonium nitrogen (NH4-N), phosphates (PO4-P) and total phosphorus (Tot-P) was monitored in all sub-studies. All types of biochar and all particle sizes of pine-spruce biochar achieved a high degree of removal of organic material (COD > 90%). Removal of Tot-P and PO4-P was higher in willow biochar and activated biochar (>70%) than in pine-spruce biochar during the first two months, but then decreased to similar levels as in pine-spruce biochar. Among the particle sizes tested, 0.7 mm pine-spruce biochar showed the lowest amount of Tot-P removal, while 2.8 mm pine-spruce biochar showed the lowest level of NH4-N removal. Different OLRs and HLRs did not influence COD removal (94–95%). Pine-spruce biochar showed a better degree of removal of Tot-N than sand. In conclusion, biochar is a promising filter medium for onsite wastewater treatment as a replacement or complement to sand, achieving high and robust performance regardless of the parent material, particle size or loading conditions.

Epidemiological Evidence and Health Risks Associated With Agricultural Reuse of Partially Treated and Untreated Wastewater: A Review

The use of partially treated and untreated wastewater for irrigation is beneficial in agriculture but may be associated with human health risks. Reports from different locations globally have linked microbial outbreaks with agricultural reuse of wastewater. This article reviews the epidemiological evidence and health risks associated with this practice, aiming toward evidence-based conclusions. Exposure pathways that were addressed in this review included those relevant to agricultural workers and their families, consumers of crops, and residents close to areas irrigated with wastewater (partially treated or untreated). A meta-analysis gave an overall odds ratio of 1.65 (95% CI: 1.31, 2.06) for diarrheal disease and 5.49 (95% CI: 2.49, 12.10) for helminth infections for exposed agricultural workers and family members. The risks were higher among children and immunocompromised individuals than in immunocompetent adults. Predominantly skin and intestinal infections were prevalent among individuals infected mainly via occupational exposure and ingestion. Food-borne outbreaks as a result of crops (fruits and vegetables) irrigated with partially or untreated wastewater have been widely reported. Contamination of crops with enteric viruses, fecal coliforms, and bacterial pathogens, parasites including soil-transmitted helminthes (STHs), as well as occurrence of antibiotic residues and antibiotic resistance genes (ARGs) have also been evidenced. The antibiotic residues and ARGs may get internalized in crops along with pathogens and may select for antibiotic resistance, exert ecotoxicity, and lead to bioaccumulation in aquatic organisms with high risk quotient (RQ). Appropriate mitigation lies in adhering to existing guidelines such as the World Health Organization wastewater reuse guidelines and to Sanitation Safety Plans (SSPs). Additionally, improvement in hygiene practices will also provide measures against adverse health impacts.

Greywater characterization and generation rates in a peri urban municipality of a developing country

The quantity and quality of combined greywater from houses with in-house water supply and houses that rely on external sources of a peri-urban area in a developing country were determined. Data for quantity of greywater was collected from 36 households while 180 samples of greywater were collected from 60 households between December 2016 and February 2017. The results indicate that, average water consumption from households with in-house access was 82.51 ± 12.21 Lc^-1d^-1 while households which rely on external sources was 36.64 ± 4.31 Lc^-1d^-1 with return factors of 74.16% and 88.57% respectively. Quality analysis also showed significant differences between greywater from the two sources with most of the quality parameters exceeding the regulatory limit. The ratio between biochemical oxygen demand (BOD₅) and chemical oxygen demand (COD) ranged between 0.22 and 0.59 for greywater from in-house sources and 0.23-0.62 for external sources indicating low biodegradability of the greywater. The nutrients recorded exceeded the trigger levels for eutrophication while significant levels of microorganisms such as E. Coli and Salmonella spp. were also detected in both streams. Direct reuse of greywater for irrigation was found to be unsuitable based on the salinity and sodium hazard analysis. Principal component analysis of the data indicated that the characteristics of the combined greywater in the study area is influenced by cooking and cleaning practices, personal hygiene, biodegradability, frequency of water use before disposal and sanitary practices in the bathroom. The greywater discharged is detrimental to the environment and poses a health risk to humans and livestock. There is therefore the need for authorities involved to prioritize greywater management and treatment in peri-urban areas of developing countries.