Rapid urbanization and population growth have increased sewage generation, creating major environmental and public health challenges, particularly in regions lacking centralized treatment. Conventional systems are effective but costly and energy-intensive, limiting decentralized deployment. Integrating water hyacinth (Eichhornia crassipes) into hydroponic systems offers a low-cost, nature-based alternative for nutrient and organic removal. This review makes three key contributions: (i) it defines a quantitative design–performance envelope linking hydraulic retention time, plant density, and harvesting frequency to treatment efficiency; (ii) it reframes biomass harvesting as a core process control governing net nitrogen and phosphorus removal and root-zone oxygen dynamics; and (iii) it integrates reactor design, biosecurity, and biomass valorization into a unified framework for decentralized sewage treatment. Synthesis of 220 studies shows that controlled floating hydroponic systems typically achieve 50–90% total nitrogen, 60–95% total phosphorus, and 60–95% BOD removal at 7–30 days HRT, driven by coupled plant uptake, rhizosphere nitrification–denitrification, and biofilm adsorption. Pathogen removal is generally limited to 0.5–2 log reductions for indicator bacteria (total and faecal coliforms/Escherichia coli), indicating that post-treatment polishing (UV, chlorination, maturation ponds, or wetlands) is required depending on the intended reuse or discharge standard. Performance declines below 15°C without greenhouse protection or hybridization with conventional biological units. Key constraints include seasonal metabolic limitations, hydraulic sensitivity to shock loading, invasive escape risks, and the need for standardized protocols for metal-laden biomass management. Proposed solutions include adaptive harvesting regimes, modular plug-flow layouts, hybrid treatment trains, and biochar production to stabilize contaminants and enable carbon sequestration. Positioned between passive wetlands and energy-intensive membrane systems, water hyacinth hydroponics offers moderate land demand, low energy use (0.02–0.1 kWh m⁻³), and circular bioeconomy potential for scalable decentralized sewage treatment.

Microalgae-based wastewater treatment is an alternative to physico-chemical and bacteria-based technologies. Microalgae-based wastewater treatment showed enormous potential, not only exhibiting excellent pollutant removal efficiencies but also unlimited opportunities for resource recovery. Despite its promising future, the question of selecting autotrophy or heterotrophy regimes for optimal organic pollutant removal remains. This current work juxtaposes the performance of autotrophic and heterotrophic cultures in treating organic-rich wastewater to shed light on the unsolved puzzle. This review paper details the autotrophy and heterotrophy growth regimes for microalgae, as well as highlights the source of organic-rich wastewater and its characteristics. A clear comparison between both regimes was then discussed with recent references. Heterotrophic cultures showed better parameter removal performances, especially carbon-related and N-related compounds, while the removal of P-related compounds is considerably similar. Heterotrophic regimes also resulted in higher biomass yield with higher P content as compared to autotrophy. Despite their superiority, heterotrophic regimes continuously require additional carbon sources, posing a cost-related limitation. In contrast, autotrophic culture has an added value of carbon sequestration, making it beneficial for climate mitigation and lowering operational costs. Future research should concentrate on techno-economic and cost-benefit analyses to further refine the currently discussed topic.

Hexavalent chromium is one of the toxic metals in water pollution. This study is aimed at analyzing the involvement of chromium reductase and biosorption potential in chromium-resistant species of Bacillus cereus. A total of 10 % (v/v) of B. cereus biomass was inoculated into a 90 mL chromium-contaminated solution with an initial concentration of 60 mg/L. Biomass digestion was carried out every day for a 5-day treatment period for chromium content analysis, while biomass characterization was carried out at the end of the treatment period, comparing the exposed vs. non-exposed bacteria. Results indicated that the highest chromium removal (16.12 ± 0.63 %) was obtained on day 3, while the maximum biosorption capacity was obtained on day 1, reaching 0.461 ± 0.02 mg Cr/g dry cell of biomass. XRD showed the crystalline structure of the bacteria cell after being exposed to chromium, suggesting that interactions between polysaccharides and proteins in the membrane may occur during the treatment. In addition, FT-IR spectra also showed decreasing peaks and the involvement of hydroxyl, carboxyl, carbonyl, and nitroxide groups during the treatment. SEM-EDX results indicated that bacteria are experiencing cell structure alteration with more intense chromium spectra on the surface, while TEM images showed endospore formation by B. cereus under adverse environmental conditions. This study suggested that the removal of hexavalent chromium by B. cereus might be dominant via biosorption (translocated into cell biomass).

Tofu effluent contains a high concentration of organic materials, nutrients, suspended solids and is also low in pH. This research was aimed at applying phytotreatment using floating plant species of Pistia stratiotes to polish tofu effluent before final discharge into water bodies while also producing biogas from the resultant biomass after treatment. A range-finding test (RFT) was conducted to determine the initial concentration to be treated and resulted in 10 % tofu effluent. Phytotreatment was conducted for a period of 14 days, focusing on the removal of organic matter and nutrient contents. After 14 days of treatment, P. stratiotes were able to remove total suspended solids (TSS) by 88 %, ammonia by 42.3 %, phosphate by 50 %, chemical oxygen demand (COD) by 84 %, and biological oxygen demand (BOD) by 95 %, significantly higher as compared to control. Phytotreatment was able to stabilize pH to a neutral value, and P. stratiotes were able to transfer oxygen from air to the rhizosphere area. The maximum daily production of biogas using the plant's biomass was higher as compared to the control; however, the overall biogas accumulation was significantly lower during the 45 days of observation. Further biomass pretreatment was suggested before digestion to obtain higher biogas production since the cellulose, hemicellulose, and lignin content inside the plant biomass were subjected to being hardly degraded by the anaerobic microorganisms.