A pilot anaerobic bioreactor requires near-daily monitoring and frequent maintenance. This study aimed to upgrade a pilot bioreactor into a low-cost IoT device via ESP32 microcontrollers. The methodology was based on remote data acquisition and online monitoring of various parameters towards assessing the anaerobic digestion performance. A semi-continuous tank bioreactor with a 60 L total volume was initially inoculated mainly with livestock manure and fed daily with a mixture of glucose, gelatin, and oleic acid, supplemented with a basic anaerobic medium. Under steady-state conditions, the organic loading rate was 2 g VS L_R⁻¹ d⁻¹. Sensors for pH, temperature, REDOX potential, and ammonium concentration, along with devices measuring biogas volume and methane content, were integrated and validated against analytical methods. Biogas production was recorded accurately, enabling the early detection of production declines through ex-situ data analysis. Methane concentration variance was less than 6% compared to gas chromatography, while temperature and pH deviations were 0.15% and 1.67%, respectively. Ammonia ion measurements required frequent recalibration due to larger fluctuations. This IoT-enhanced system effectively demonstrated real-time monitoring of critical bioreactor parameters, with ESP32 enabling advanced control and monitoring capabilities.

This study investigated the effect of light intensity on the growth and nutrient uptake of Chlorella sorokiniana cultivated in nitrogen-rich anaerobic digestion wastewater. Three light intensities (20, 68, and 162 µmol m⁻² s⁻¹) were applied over a 30-day period with a 16:8 h light–dark photoperiod. The goal was to understand how light affects biomass productivity, nutrient assimilation, and biochemical composition under varying nitrogen concentrations originating from biogas plant digestate, up to 5 g L⁻¹. The results showed that higher light intensities significantly boosted biomass production, achieving a five-fold increase at 162 µmol m⁻² s⁻¹ compared to 20 µmol m⁻² s⁻¹. Nutrient uptake followed a similar pattern, with 94% of ammonium nitrogen removed in 7 days under high light, compared to 55% after 30 days under low light. Phosphorus content was also completely removed after 7 days under light intensities of 68 and 162 µmol m⁻² s⁻¹. Additionally, elevated light intensity led to increased lipid accumulation (from 29.7% to 34%) and reduced protein content (from 30.9% to 26.1%), with carbohydrate content not being affected by light intensity. These findings highlight light intensity as a critical factor for optimizing microalgae cultivation in nitrogen-rich biogas digestate, promoting both effective nutrient removal and biomass production for potential bioenergy applications.

BACKGROUND: Microbial consortia resistant to high ammonia concentrations may facilitate biogas production from high ammonia‐containing wastes and manures during anaerobic digestion. Microbial communities were gradually enriched via sequential batch cultivations (stepwise exposure) at increasing ammonia concentrations up to the extremely high concentration of 9 g total ammonia nitrogen (TAN) L⁻¹. This study examined the adaptation of anaerobic microbial consortia to high ammonia concentrations by the use of a complex substrate based on manure in order to generate tailor‐made inocula for bioaugmentation purposes. RNA analysis was performed to determine the microbial community composition and activity of anaerobic bacteria and methanogens.RESULTS: The enrichment series was successful in terms of methane production at ammonia concentrations as high as 5 g TAN L⁻¹ in comparison with the control concentration of 2 g TAN L⁻¹. Methanosarcina was the core active dominant methanogen genus in all enrichment cultures and its relative activity was sharply increased at 3 g and 9 g TAN L⁻¹. Cellulolytic bacteria activity mostly decreased with ammonia increase. Moreover, syntrophic butyrate and long‐chain fatty acid degraders along with hydrogenotrophic methanogens were activated at increased ammonia concentrations.CONCLUSIONS: The results of the study demonstrated an efficient method to enrich ammonia‐tolerant microbial consortia for bioaugmentation purposes in biogas reactors with concentrations ≤5 g TAN L⁻¹. RNA analysis revealed high relative abundances of Methanosarcina and hydrogenotrophic methanogens at high concentrations of ammonia. © 2020 Society of Chemical Industry

Ammonia accumulation in biogas plants reactors is becoming more frequently encountered, resulting in reduced methane (CH₄) production. Ammonia toxicity occurs when N-rich substrates represent a significant part of the biogas plant’s feedstock. The aim of this study was to develop an estimation method for the effect of ammonia toxicity on the CH₄ production of biogas plants. Two periods where a biogas plant operated at 3200 mg·L⁻¹ (1st period) and 4400 mg·L⁻¹ (2nd period) of ammonium nitrogen (NH₄⁺–N) were examined. Biomethane potentials (BMPs) of the individual substrates collected during these periods and of the mixture of substrates with the weight ratio used by the biogas plant under different ammonia levels (2000–5200 mg·L⁻¹ NH₄⁺–N) were determined. CH₄ production calculated from the substrates’ BMPs and the quantities used of each substrate by the biogas plant was compared with actual CH₄ production on-site. Biogas plant’s CH₄ production was 9.9% lower in the 1st and 20.3% in the 2nd period in comparison with the BMP calculated CH₄ production, of which 3% and 14% was due to ammonia toxicity, respectively. BMPs of the mixtures showed that the actual CH₄ reduction rate of the biogas plant could be approximately estimated by the ammonia concentrations levels.

Wastewater treatment plants have been traditionally developed for the aerobic degradation of effluent organic matter, and are associated with high energy consumption. The adoption of sustainable development targets favors the utilization of every available energy source, and the current work aims at the identification of biomethane potential from non-conventional sources derived from municipal wastewater treatment processes. Byproducts derived from the primary treatment process stage were collected from four sewage treatment plants in Greece with great variation in design capacity and servicing areas with wide human activities, affecting the quality of the influents and the corresponding primary wastes. The samples were characterized for the determination of their solids and fats content, as well as the concentration of leached organic matter and nutrients, and were subjected to anaerobic digestion treatment for the measurement of their biomethane production potential according to standardized procedures. All samples exhibited potential for biogas utilization, with screenings collected from a treatment plant receiving wastewater from an area with combined rural and agro-industrial activities presenting the highest potential. Nevertheless, these samples had a methanogens doubling time of around 1.3 days, while screenings from a high-capacity unit proved to have a methanogens doubling time of less than 1 day. On the other hand, floatings from grit chambers presented the smallest potential for energy utilization. Nevertheless, these wastes can be utilized for energy production, potentially in secondary sludge co-digestion units, converting a treatment plant from an energy demanding to a zero energy or even a power production process.

Agricultural product drying is of great importance as it is a reliable method for fruit and vegetable preservation. Tackling the high energy consumption of the process will reduce the final product cost and mitigate greenhouse gas emissions. In this work, a passive drying method was experimentally evaluated. The method was based on the principle of the stack effect taking place in the solar chimney structure. Different types of solar chimneys in terms of dimensions and materials were evaluated for the drying of banana and potato slices. The results of the experiments showed that the drying rate was close to solar drying systems. Parameters such as height and material characteristics of drying tubes, as also weather conditions, influenced the drying rate. It was found that the banana and potato slices were dried at a satisfactory rate for almost 48 h during the summer period in Greece. From the parameters of the drying tubes that were varied, it was found that both the height and material played a major role, as did the air flow rate. With the increase in the drying tube by 1 m and with the choice of proper manufacturing material, an increase in the flow rate between 40% and 100% can be achieved. When only the color of two 3 m-high tubes changed, the flow rate varied between 4% and 15%. The proposed method has almost zero energy consumption, and it could be used as a standalone or as a part of a hybrid drying system. It can also be adjusted in existing greenhouse-type agricultural structures as a parallel operation system.