The research team, led by scientists at Cadi Ayyad University in Marrakech in collaboration with partners in Switzerland, China, Germany, Tunisia and Saudi Arabia, built a vertical-flow constructed wetland fed with wastewater that had already passed through natural lagooning at the Sâada treatment plant near Marrakech. The pilot unit, a cylindrical container roughly 0.9 meters tall with a surface area of 2.17 square meters, was planted with common reed (Phragmites australis) and layered with gravel, sand and, crucially, a biochar layer produced by slow pyrolysis of olive branches at 500 degrees Celsius. The system ran continuously for four months under real-world conditions.

Biochar is the carbon-rich solid left behind when biomass is heated in a low-oxygen environment. Its appeal in water treatment lies in its enormous surface area, its porous structure and its wealth of surface functional groups that can bind pollutants. The olive-derived biochar in this study proved exceptional: elemental analysis showed a carbon content of 92.11 percent by mass, well above the 50 to 85 percent typically reported for biochars made at moderate temperatures, and an exceptionally low oxygen-to-carbon ratio of 0.086, a signature of high stability and long-term resistance to microbial degradation.

Scanning electron microscopy revealed a highly porous, heterogeneous architecture riddled with pores of varying sizes and remnants of the original plant’s vascular structure, creating an intricate network for trapping contaminants. Infrared spectroscopy identified strong signals from aromatic carbon structures and oxygenated functional groups such as hydroxyl, carboxyl and phenolic moieties. Together, these features give the biochar multiple parallel routes for capturing pollutants: hydrophobic and pi-pi interactions for aromatic drug molecules, electrostatic attraction and complexation for metal ions, and simple physical entrapment for larger particles and bacteria.

The removal figures for toxic metals were striking. Arsenic concentrations fell from 16.35 micrograms per liter at the lagoon outlet to 2.75 micrograms per liter after the wetland, a 91 percent reduction. Cadmium dropped from 0.0936 to 0.0014 micrograms per liter and lead from 0.6036 to 0.089 micrograms per liter, corresponding to removal efficiencies of 99.998 percent and 99.84 percent respectively. The authors attribute this performance to surface complexation with oxygen-containing functional groups and precipitation as insoluble metal hydroxides or carbonates in the mildly alkaline environment that the biochar helps maintain.

Pharmaceutical residues posed a tougher test because their chemistry varies widely. The system nonetheless delivered removal rates ranging from 63 percent to more than 99 percent depending on the compound. Ibuprofen and ciprofloxacin were cut by 96 to 97 percent, paracetamol was eliminated almost entirely, and even notoriously recalcitrant molecules such as carbamazepine and diclofenac were reduced by more than 60 percent. For comparison, conventional wetlands without biochar typically achieve only 40 to 60 percent removal for most pharmaceuticals, and carbamazepine removal in conventional systems often falls below 20 percent. The authors estimate that biochar addition improved performance by factors of roughly 1.3 to 3.2 depending on the drug.

Perhaps the most consequential result concerns antibiotic resistance. Using quantitative polymerase chain reaction, the team tracked genes encoding beta-lactamase enzymes, including blaTEM, blaSHV and blaCTX-M, which are major drivers of antibiotic resistance in clinical settings. Abundance of these genes, normalized to the universal 16S rRNA gene, fell by one to four orders of magnitude after treatment, with blaCTX-M showing the largest decline of roughly three to four orders of magnitude. Bacterial indicators fell in parallel: Escherichia coli dropped by 79 percent, enterococci by more than 93 percent, while Pseudomonas species, which are environmental rather than fecal organisms, proved more resistant to removal at about 47 percent.

The differential removal of resistance genes offers clues about mechanism. The authors suggest that genes carried on mobile plasmids, such as blaCTX-M, may be more vulnerable because their host bacteria are more susceptible to the wetland’s filtration and inactivation processes, whereas chromosomally encoded genes in hardier environmental bacteria persist longer. Physical retention of gene-carrying bacteria within the biochar’s porous structure, inactivation under unfavorable substrate conditions, and adsorption of extracellular DNA fragments onto positively charged biochar surfaces likely all contribute. The researchers caution that the precise mechanisms require further investigation through metagenomics and gene-tracking studies.

Conventional water quality parameters also improved markedly. Suspended solids fell by 83.7 percent, chemical oxygen demand by 75.7 percent, total phosphorus by 77.8 percent and orthophosphates by 76.7 percent, figures that meet or exceed the upper range reported in meta-analyses of standard constructed wetlands. Nitrate and nitrite removals of 68.9 and 75.4 percent point to active coupled nitrification and denitrification, aided by the oxygen gradients created by reed roots and the alternating aerobic and anaerobic zones of the layered substrate. The treated effluent met Moroccan irrigation standards for suspended solids, nutrients and heavy metals, with arsenic at just 2.75 percent of the FAO limit and cadmium and lead at fractions of a percent of their thresholds.

The study is not without caveats. The team did not run a side-by-side control wetland without biochar, relying instead on literature benchmarks, and they did not measure the biochar’s surface area by gas adsorption, leaving quantitative structure-performance relationships unestablished. One anomaly, a sharp increase in valsartan acid, a metabolite of the blood-pressure drug valsartan, suggests desorption or transformation processes that warrant further study. Residual pharmaceutical concentrations of tens to hundreds of nanograms per liter remain in the effluent, and the authors recommend additional disinfection to meet WHO criteria for unrestricted irrigation, along with long-term monitoring of crop uptake and soil health. Still, with an estimated biochar lifespan of 12 to 18 months, a feedstock that is abundant agricultural waste across the Mediterranean, and performance that rivals far more energy-intensive tertiary technologies such as ozonation, the system presents a compelling case that the solution to some of wastewater treatment’s most stubborn problems may lie in a layer of charcoal and a stand of reeds.

Subject of Research: Biochar-enhanced constructed wetlands for removing heavy metals, pharmaceuticals and antibiotic resistance genes from municipal wastewater

Article Title: Synergistic removal of various emergent pollutants in biochar-enhanced constructed wetlands: a pilot-scale nature-based solution for municipal wastewater treatment improvements

Article References: Synergistic removal of various emergent pollutants in biochar-enhanced constructed wetlands: a pilot-scale nature-based solution for municipal wastewater treatment improvements. (n.d.). https://doi.org/10.3389/fenvc.2026.1762724

Image Credits: AI Generated

DOI: 10.3389/fenvc.2026.1762724

Keywords: biochar, constructed wetland, wastewater treatment, heavy metals, pharmaceutical residues, antibiotic resistance genes, Phragmites australis, water reuse, nature-based solution, pilot scale, Morocco, olive waste

The appeal of waste apples as a fermentation feedstock lies in their biochemical makeup. Spoiled Jonagold apples supplied by Werder Frucht GmbH and prepared at ATB were pressed into a sugar-rich mash containing about 71.6 grams per liter of fructose, 21.5 grams per liter of glucose, and 7.5 grams per liter of sucrose, along with a high moisture content of 88.9 percent. Unlike apple pomace, the fibrous solid residue left after juice extraction that has dominated previous research, the mash retains readily fermentable simple sugars and requires minimal pretreatment. The solid fraction, composed mainly of peel and seeds, was excluded from the study. This compositional simplicity matters because lignocellulosic residues typically demand energy-intensive pretreatment to release their sugars and often generate inhibitory by-products that slow microbial growth.

Before fermentation could begin, the researchers needed to prepare the mash as a workable medium. They tested several commercial enzyme preparations, including Pectinase L40, Cellic CTec3 HS, Dextrozyme GA, and Viscoferm, at the mash’s natural pH of 4.5 and a temperature of 50 degrees Celsius. Surprisingly, none of the enzymes significantly increased the total reducing sugar content compared with an untreated control, a result the team attributes to the absence of starch in ripe apples and the low levels of cellulose and hemicellulose in the dry matter. However, Cellic CTec3 HS produced a marked reduction in viscosity, which is critical for fermentation because thick media impede mass transfer, create gradients of pH, temperature, and nutrients, and complicate downstream separation. The researchers ultimately selected a low-dose combination of Pectinase L40 and Cellic CTec3 HS, each at 0.5 milliliters of enzyme per kilogram of biomass, to liquefy the mash for subsequent microbial screening.

With a liquefied substrate in hand, the team screened microbial candidates for both target products. For lactic acid, five strains of Heyndrickxia coagulans, formerly known as Bacillus coagulans, were drawn from ATB’s internal collection of 700 isolates. Optical density measurements in apple mash medium, with and without yeast extract supplementation, identified strains A35, A138, and A203 as the strongest performers. For succinic acid, the researchers compared Actinobacillus succinogenes DSM 22257 against several strains of Basfia succiniproducens, confirming earlier reports that A. succinogenes converts both pentose and hexose sugars to succinic acid with superior yields. Subsequent bioreactor screening at 0.25 liters showed that all three H. coagulans strains produced lactic acid at similar concentrations, between 71.8 and 75.5 grams per liter, with yields of 0.91 to 0.94 grams per gram of sugar consumed. Strain A203, however, achieved the highest productivity at 3.5 grams per liter per hour and showed no lag phase, making it the clear choice for scale-up.

Nutrient availability emerged as a decisive factor in both fermentations. When yeast extract was omitted, lactic acid production by H. coagulans A203 collapsed to 32.3 grams per liter after 49 hours, with productivity falling to 0.7 grams per liter per hour. The effect was even more dramatic for A. succinogenes, whose succinic acid output dropped from 35.6 to 6.7 grams per liter without supplementation. These results indicate that apple mash, despite its abundant sugars, lacks sufficient nitrogen and growth factors to sustain industrial fermentation performance. The authors note that replacing yeast extract with cheaper agro-industrial nitrogen sources, such as wine lees or tomato pomace, represents a promising avenue for reducing production costs, since nutrient supply is one of the main economic burdens in biobased organic acid manufacturing.

The central innovation of the study lies in what the researchers removed from the process rather than what they added. Conventional bioprocesses typically separate the enzymatic hydrolysis and fermentation stages with centrifugation to remove solids and sterilization, usually at 121 degrees Celsius under pressure, to eliminate contaminants. Each of these steps adds capital cost, energy demand, and processing time. Instead, the team performed enzymatic liquefaction and fermentation sequentially in the same vessel. For lactic acid, no sterilization was needed at all because H. coagulans A203 is thermophilic, growing optimally at 50 degrees Celsius, a temperature that suppresses most contaminating microbes and shortens the fermentation window. For succinic acid, where A. succinogenes prefers a mesophilic 37 degrees Celsius, the researchers inserted a simplified thermal inactivation step, heating the mash to 80 to 85 degrees Celsius for 15 minutes, which denatures the proteins and disrupts the membranes of most spoilage organisms without the energy burden of full autoclaving.

After validating this simplified procedure at 1-liter laboratory scale, where it matched the performance of the conventional approach with no significant differences in concentration, yield, or productivity, the team moved to pilot scale. Lactic acid fermentation was carried out in a 30-liter working volume using 30 kilograms of apple mash in a Biostat UD bioreactor. The process delivered 73.8 grams per liter of lactic acid with a yield of 0.91 grams per gram of sugar consumed and a productivity of 2.7 grams per liter per hour. Remarkably, the final product exhibited an optical purity of 99.7 percent L-lactic acid, a strong indicator that contamination never took hold, since contaminating bacteria typically produce a mixture of L- and D-isomers. The overall product yield reached 0.78 grams of lactic acid per gram of apple mash on a dry basis, and the bacteria also consumed the malic acid naturally present in the fruit.

The succinic acid pilot run, conducted with 20 kilograms of apple mash in a 25-liter working volume, produced 36.8 grams per liter of succinic acid with a yield of 0.69 grams per gram and a productivity of 1.0 gram per liter per hour, alongside acetic and formic acids as natural by-products of A. succinogenes metabolism. Notably, the strain fixed carbon dioxide during succinate formation, an inherent environmental advantage of the process. These figures compare favorably with previous pilot-scale succinic acid fermentations using other food wastes: oat pomace with acid whey yielded only 19.6 grams per liter at 0.27 grams per liter per hour, while industrial candy waste reached 38.99 grams per liter. The lactic acid results similarly outperformed earlier work on apple pomace hydrolysate, which achieved just 40.72 grams per liter at a productivity of 0.58 grams per liter per hour, and mixed food waste, which produced 68.5 grams per liter at a yield of only 0.38 grams per gram of total solids.

Beyond the headline numbers, the study carries significant implications for how biorefineries handle agri-food waste. Retaining solids in the reactor eliminates an intermediate solid-liquid separation step, meaning only a single separation is needed after fermentation, when microbial biomass must be removed regardless of process configuration. Avoiding intermediate autoclaving also prevents heat-induced degradation of sugars and proteins, limiting the formation of unwanted by-products that complicate downstream purification, which is widely regarded as the economic bottleneck of large-scale bioproduction. Economically, waste apples serve as a zero- or low-cost feedstock that displaces commercial sugars and sidesteps the expensive pretreatment required for lignocellulosic biomass. Environmentally, the simplified process reduces energy consumption and carbon dioxide emissions, the high moisture content of the mash minimizes water input, and diverting spoiled fruit from landfill avoids methane generation.

The authors frame their work as a template for integrating agri-food residues into a circular bioeconomy, in line with the European Union’s Bioeconomy Strategy and Waste Framework Directive. They point toward future advances in intelligent biorefineries that use artificial intelligence and machine learning to adapt fermentation conditions to feedstock variability, as well as genetically engineered microbial strains designed to boost fermentation rates and product diversity. For now, the demonstration that a pilot-scale bioreactor can convert 30 kilograms of rotten apples into nearly 74 grams per liter of high-purity lactic acid marks a tangible step toward turning one of agriculture’s most familiar waste streams into a dependable industrial resource.

Subject of Research: Pilot-scale biotechnological production of lactic and succinic acids from waste apples

Article Title: Upcycling waste apples into platform chemicals: pilot-scale production of lactic and succinic acids

Article References: Portugal Rios da Costa Pereira, L., Schneider, R., Olszewska-Widdrat, A., Sturm, B., & Kaetzl, K. (2026). Upcycling waste apples into platform chemicals: pilot-scale production of lactic and succinic acids. Biotechnology for Biofuels and Bioproducts, 19(1), Article 67. https://doi.org/10.1186/s13068-026-02807-w

Image Credits: AI Generated

DOI: 10.1186/s13068-026-02807-w

Keywords: waste apples, lactic acid, succinic acid, fermentation, pilot scale, biorefinery, circular bioeconomy, Heyndrickxia coagulans, Actinobacillus succinogenes, agri-food waste, platform chemicals, bioplastics