The effects of microalgae use as a biofertilizer on soil and plant before and after its anaerobic (co-)digestion with food waste.

The increase in food waste generation has resulted in significant challenges for its sustainable management. Anaerobic digestion coupled with microalgae-based ponds for digestate treatment can be used as a low-cost eco-friendly technology approach. In this case, microalgal biomass harvested from the ponds may be valorized into bioenergy (biogas) and soil conditioner and/or biofertilizers. The aim of the present study was to evaluate the microalgal biomass produced from a food waste digestate treatment ponds as agricultural fertilizer. For this purpose, microalgal biomass was tested before and after anaerobic digestion and co-digestion with food waste, exploring its potential for valorization. The inorganic fertilizer urea and soil with no fertilization were also used as treatments. The experimental design consisted of applying the treatments in pots cultivated with hybrid grass Brachiaria cv. Sabiá and distributed in randomized blocks in a controlled greenhouse. Microalgal biomass was mainly composed by Scenedesmus sp.. The assessed parameters showed comparable results on plant growth (i.e. number of tillers, fresh and dry matter and Chlorophyll content index) for fresh and digested microalgal biomass and inorganic fertilizer. Furthermore, it was observed that fresh microalgae provided the highest Phosphorus content in the leaf (21 %). Additionally, there were increases of 9 % in Nitrogen and 12 % in organic matter in the soil after applying digested microalgae compared to the control group without any fertilization. Finally, experimental data obtained suggests that microalgae-based biofertilizer holds the potential to replace inorganic fertilizer as a nutrient source. Moreover, it contributes to the valorization of by-products from organic waste treatment.

Nature-based solutions for wastewater treatment and bioenergy recovery: A comparative Life Cycle Assessment.

The aim of this study was to assess the environmental impacts of up-flow anaerobic sludge blanket (UASB) reactors coupled with high rate algal ponds (HRAPs) for wastewater treatment and bioenergy recovery using the Life Cycle Assessment (LCA) methodology. This solution was compared with the UASB reactor coupled with other consolidated technologies in rural areas of Brazil, such as trickling filters, polishing ponds and constructed wetlands. To this end, full-scale systems were designed based on experimental data obtained from pilot/demonstrative scale systems. The functional unit was 1 m3 of water. System boundaries comprised input and output flows of material and energy resources for system construction and operation. The LCA was performed with the software SimaPro®, using the ReCiPe midpoint method. The results showed that the HRAPs scenario was the most environmentally friendly alternative in 4 out of 8 impact categories (i.e. Global warming, Stratospheric Ozone Depletion, Terrestrial Ecotoxicity and Fossil resource scarcity). This was associated with the increase in biogas production by the co-digestion of microalgae and raw wastewater, leading to higher electricity and heat recovery. From an economic point of view, despite the HRAPs showed a higher capital cost, the operation and maintenance costs were completely offset by the revenue obtained from the electricity generated. Overall, the UASB reactor coupled with HRAPS showed to be a feasible nature-based solution to be used in small communities in Brazil, especially when microalgae biomass is valorised and used to increase biogas productivity.

Long-term operation of anaerobic digestion of food waste under simplified conditions: effect on reactor performance.

Anaerobic digestion under simplified conditions can contribute to food waste decentralised management. However, there is an absence of knowledge on the effect of long-term operation under these conditions. This study aimed to evaluate the operational conditions of an anaerobic reactor treating food waste after long-term operation without temperature control and low-intensity mixing. For this, a demonstration-scale reactor (18.8 m3) was operated for 160 days, while stability parameters were used to control the applied organic loading rate (OLR). Stability parameters indicated that the reactor was operated at stable conditions with an OLR of 0.3 kg VS m-3 d-1, while it was overloaded at an OLR of 0.4 kg VS m-3 d-1. This was observed through high value of intermediate and partial alkalinity ratio (IA/PA ratio), 2.5, and low values of bicarbonate alkalinity and pH, 1800 mg CaCO3 L-1 and 6.8, respectively. Moreover, there was a change in the concentration of intermediated metabolites, with a higher content of propionate and acetate, 1080 and 3775 mg L-1, respectively. Consequently, the methane production rate was decreased from 0.12 to 0.08 m3 CH4 m-3 d-1 and methane yield from 0.43 to 0.15 m3 CH4 kg VS-1. The reactor instability at a relatively low OLR was most probably due to hydrodynamic factors caused by the accumulation of recalcitrant material. Therefore, this material reduced the reactor performance and requires attention for a sustainable long-term operation.

Public toilets from the perspective of users: a case study in a public place, Brazil.

Public toilets are essential infrastructure to guarantee the right to sanitation in public spaces and, in more general terms, the right to inclusive and sustainable cities. Moreover, since the equipment has a direct user interface, it is important to understand their demands and needs. Given this, the present research aims to understand the perspective of public toilet users on the Pampulha Lake Shore (PLS), a public touristic place in Belo Horizonte, Brazil. For that, observations and semi-structured interviews were carried out with different public toilet users. In addition, comments posted on the Google Local Guides tool of Google Maps were used as a secondary database for understanding users' experience of PLS toilets. The analysis made it possible to identify aspects related to availability, quality (health and hygiene), security, and accessibility. Collected data showed how the conflicting choice of whether or not to use the toilet was directly related to the health and conservation of the urban equipment and interfered with social and leisure prospects. On the whole, the importance of the user's perspective was highlighted in this study with emphasis on elaborating adequate urban planning with regard to health, sanitation, and accessibility issues.

Effect of digestate loading rates on microalgae-based treatment under low LED light intensity.

Low red-LED irradiances are an attractive alternative for enhancing microalgae photobioreactors treating digestate due to their potential contribution in decreasing area footprints with low energy consumptions. However, more information is required regarding the influence of digestate load on treatment performance and biomass valorisation when low-intensity red-LEDs are applied. Thus, this study assessed microalgae-based photobioreactors treating food waste digestate under different concentrations (5%, 25%, 50%, and 75%, v/v) at low red-LED irradiance (15 µmol·m-2·s-1). The removal efficiencies of soluble chemical oxygen demand (sCOD) at the end of the experiment ranged from 45% to 75% when treating influent loads between 5.3 and 79.1 g sCOD·m-3·d-1 (5% and 75%-digestate), respectively. Total ammonia nitrogen (TAN) was applied in loading rates between 3.2 and 48.5 g TAN·m-3·d-1 (5% and 75%, respectively) and removed with maximum efficiencies of 90%-100% in all trials. Nitrification-denitrification was proportionally more relevant when treating 5%-digestate, whereas volatilisation was the primary process in 25%, 50% and 75% concentrations. Microalgae presented adequate yields in all treatments, except in 75%-digestate, likely due to the blocking of light by the high solids concentrations. The assessment of the microalgae community and chlorophyll-a and carotenoids suggested that chlorophytes, mainly Dictyosphaerium pulchellum and Scenedesmus sp. grew autotrophically, whereas cyanobacteria Pseudanabaena sp. grew mixotrophically. Moreover, the sustainability of red LED lighting applications can be increased by anaerobic digestion or agricultural valorisation of the biomass, enabled by its high N and P contents. Low-intensity red-LEDs may have promissory applications in the treatment of high-strength wastewaters.

The use of solar pre-treatment as a strategy to improve the anaerobic biodegradability of microalgal biomass in co-digestion with sewage.

Sustainable sewage treatment plants (STPs) have been intensively investigated in search for low-cost, environmental-friendly options. Anaerobic-aerobic treatment solutions, as upflow anaerobic sludge blanket (UASB) reactors followed by high rate algal ponds (HRAP) have already proved to be efficient for pollutants and micropollutants removal, as well as for energy recovery from the co-digestion of raw sewage and microalgal biomass. Since microalgae cells have complex structures that make them resistant to anaerobic digestion, pre-treatment techniques may be applied to improve microalgal biomass solubilisation and methane yield. Among the thermal pre-treatments, the use of solar energy for biomass solubilisation has yet to be investigated. Therefore, this study aimed at evaluating the performance of a solar thermal microalgal biomass pre-treatment prior to the anaerobic co-digestion with raw sewage, comparing a UASB reactor feed only raw sewage and other UASB reactor feed with raw sewage and pre-treated microalgal biomass. The results showed that, the solar pre-treatment step reached an organic matter solubilisation of 32% (COD). Furthermore, the methane yield was increased by 45% (from 81 to 117 NL CH4 kg-1 COD), after the anaerobic co-digestion with pre-treated microalgae as compared to the mono-digestion of raw sewage, indicating significant difference between the evaluated UASB reactors. The energy assessment showed a positive energy balance, as the total energy produced was twice the energy consumed in the system.

Can high rate algal ponds be used as post-treatment of UASB reactors to remove micropollutants?

The present study evaluated the removal capacity of a UASB-HRAP treatment system, combining anaerobic and microalgae-based, aerobic treatment, for eleven organic micropollutants present in raw sewage, including pharmaceuticals, estrogens and xenoestrogens. The UASB reactor and the HRAP were operated at a hydraulic retention time (HRT) of 7 h and 8 days, respectively. Influent and effluent samples from the UASB and HRAP were collected periodically. All the target compounds were detected in raw sewage, with an occurrence ranging from 70 to 100%. Removal rates in the UASB reactor were generally incomplete, ranging from no removal (-25.12% for the hormone EE2-ethinylestradiol) to 84.91% (E2 - estradiol). However, the overall performance of the UASB + HRAP system was highly efficient for the majority of the compounds, with removal rates ranging from 64.8% (ibuprofen) to 95% (estrone). Gemfibrozil and bisphenol A were the only exceptions, with overall removal rates of 39% and 43%, respectively. Hormones were the compounds with the highest removal rates in the system.

Upflow anaerobic sludge blanket in microalgae-based sewage treatment: Co-digestion for improving biogas production.

Upflow anaerobic sludge blanket (UASB) reactors are widely used to treat domestic sewage and frequently require post-treatment. Little is known about the use of high rate algal ponds (HRAP) for post-treating UASB reactors' effluent. This study aimed to evaluate a UASB reactor followed by a HRAP in terms of sewage treatment efficiency and biogas production, during one year at demonstration-scale. The UASB reactor co-treated raw sewage and the harvested microalgal biomass from the HRAP, which was recirculated to the reactor. An identical UASB reactor, treating only raw sewage, was used as control. The results showed an overall removal of 65% COD and 61% N-NH4 in the system. Furthermore, methane yield was increased by 25% after anaerobic co-digestion with microalgae, from 156 to 211 NL CH4 kg-1 VS. An energy assessment was performed and showed a positive energy balance, with a net ratio of 2.11 to the annual average.

Evaluation of a Combined System Based on an Upflow Anaerobic Sludge Blanket Reactor (UASB) and Shallow Polishing Pond (SPP) for Textile Effluent Treatment

Abstract Color removal from textile effluents was evaluated using a laboratory-combined process based on an upflow anaerobic sludge blanket (UASB) reactor followed by a shallow polishing pond (SPP). The anaerobic reactor was fed with a real textile effluent, diluted 10-times in a 350 mg/L solution of pre-treated residual yeast extract from a brewery industry as nutrient source. The parameters color, COD, N-NH3 and toxicity were monitored throughout 45 days of operation. According to the results, decolorization and COD removal were highest in the anaerobic step, whereas the effluent was polished in the SPP unit. The overall efficiency of the complete UASB-SPP system for COD and color were 88 and 62%, respectively. Moreover, the N-NH3 generated by the residual yeast extract ammonification was below 5 mg/L for the final effluent. Finally, no toxicity was detected after the treatment steps, as shown by the Vibrio fischeri microscale assay.

Enzymatic Pretreatment of Microalgae: Cell Wall Disruption, Biomass Solubilisation and Methane Yield Increase.

Anaerobic digestion of microalgal biomass for biogas production may be limited due to the cell wall resulting in an inefficient bioconversion. Enzymatic pretreatments are applied for inducing cell damage/lysis and organic matter solubilisation and this way increasing biogas production. We evaluated enzymatic pretreatments in different conditions for comparing in relation to cell wall rupture, increase of soluble material and increase in biogas production through anaerobic digestion performance in BMP assay. Chlorella sorokiniana cultures were subjected to three different enzymatic pretreatments, each under four different conditions of enzyme/substrate ratio, pH and application time. The results showed increases over 21% in biogas productions for all enzymatic pretreatments. Enzymatic pretreatment was effective at damaging microalgae cell wall, releasing organic compounds and increasing the rate and final methane yield in BMP tests. We observed a synergistic activity between the mixtures enzymes, which would depend on operational conditions used for each pretreatment.

Condições higiênico-sanitárias das unidades de produção de alimentos de um empreendimento econômico solidário / Hygienic-sanitary conditions of food production units of a solid economic undertaking

Objetivou-se verificar as condições higiênico-sanitárias das Unidades de Produção de Alimentos de um Empreendimento Econômico Solidário. Foi aplicada uma lista de verificação em 13 unidades, com base na RDC 275/2002 da ANVISA, no período de julho a setembro de 2018, composta por 163 itens divididos em 5 blocos: edificação e instalações; equipamentos, móveis e utensílios; manipuladores; produção e transporte dos alimentos; e documentação. As unidades do empreendimento foram classificadas no grupo III, por apresentarem percentual de adequação menor que 50,0%. Conclui-se que as unidades apresentaram condições higiênico-sanitárias deficientes, necessitando adequar-se ás Boas Práticas de Fabricação, principalmente no que diz respeito à formação das cooperadas, a fim de garantir a produção segura de alimentos.

Strategies to Optimize Microalgae Conversion to Biogas: Co-Digestion, Pretreatment and Hydraulic Retention Time.

This study aims at optimizing the anaerobic digestion (AD) of biomass in microalgal-based wastewater treatment systems. It comprises the co-digestion of microalgae with primary sludge, the thermal pretreatment (75 °C for 10 h) of microalgae and the role of the hydraulic retention time (HRT) in anaerobic digesters. Initially, a batch test comparing different microalgae (untreated and pretreated) and primary sludge proportions showed how the co-digestion improved the AD kinetics. The highest methane yield was observed by adding 75% of primary sludge to pretreated microalgae (339 mL CH4/g VS). This condition was then investigated in mesophilic lab-scale reactors. The average methane yield was 0.46 L CH4/g VS, which represented a 2.9-fold increase compared to pretreated microalgae mono-digestion. Conversely, microalgae showed a low methane yield despite the thermal pretreatment (0.16 L CH4/g VS). Indeed, microscopic analysis confirmed the presence of microalgae species with resistant cell walls (i.e., Stigioclonium sp. and diatoms). In order to improve their anaerobic biodegradability, the HRT was increased from 20 to 30 days, which led to a 50% methane yield increase. Overall, microalgae AD was substantially improved by the co-digestion with primary sludge, even without pretreatment, and increasing the HRT enhanced the AD of microalgae with resistant cell walls.

Treatment of food waste digestate using microalgae-based systems with low-intensity light-emitting diodes.

Anaerobic digestion of food wastes coupled with digestate post-treatment using microalgae-based systems could recover large amounts of energy and nutrients worldwide. However, the development of full-scale implementations requires overcoming microalgae inhibition by high ammonia concentrations and low light transmittances affecting photosynthesis. This study evaluated the potential of microalgae-based reactors supplied with red light-emitting diodes (LEDs) at low intensity (660 nm and 15 µmol·m-2·s-1) to treat food waste digestate. LED reactors were compared with control reactors exposed to solar radiation. From a range of species in the inoculum, Chlorella vulgaris showed high adaptation to both lighting regimes and digestate environmental conditions, characterized by a C:N:P ratio of 74:74:1. Removal efficiencies for control and LED reactors were 84.0% and 95.8% for soluble chemical oxygen demand (COD) and 89.4% and 53.0% for ammonia, respectively. Approximately 50% of ammonia in control reactor and 15% in LED reactor was lost from the systems, whereas 17% and 36% of ammonia was transformed to organic nitrogen in control and LED reactors, respectively. Low-intensity LEDs maintained microalgae growth in levels similar to solar radiation and supported efficient digestate treatment, showing a potential for further application in optimization of full scale reactors at a relatively low energy cost.

Anaerobic-Aerobic Combined System for the Biological Treatment of Azo Dye Solution using Residual Yeast.

This study aimed to investigate the treatment efficiency of a synthetic dye solution in an anaerobic-aerobic combined reactor system, using pretreated residual yeast as a nutrient source and redox mediator. The applicability of the residual yeast as a nutrient source was firstly evaluated in anaerobic batch tests. Subsequently, two continuous bench-scale treatment settings were studied: (1) an Upflow Anaerobic Sludge Blanket (UASB) reactor followed by an activated sludge system and, (2) a UASB reactor followed by a shallow polishing pond. The two system configurations were fed with a synthetic azo dye solution of Yellow Gold Remazol (50 mg/L) and pretreated residual yeast (350 mg/L). According to the results, the UASB/shallow polishing pond-combined reactor attained the best values of chemical oxygen demand (COD) (85%) and dye removal (23%).

Anaerobic co-digestion of coffee husks and microalgal biomass after thermal hydrolysis.

Residual coffee husks after seed processing may be better profited if bioconverted into energy through anaerobic digestion. This process may be improved by implementing a pretreatment step and by co-digesting the coffee husks with a more liquid biomass. In this context, this study aimed at evaluating the anaerobic co-digestion of coffee husks with microalgal biomass. For this, both substrates were pretreated separately and in a mixture for attaining 15% of total solids (TS), which was demonstrated to be the minimum solid content for pretreatment of coffee husks. The results showed that the anaerobic co-digestion presented a synergistic effect, leading to 17% higher methane yield compared to the theoretical value of both substrates biodegraded separately. Furthermore, thermal hydrolysis pretreatment increased coffee husks anaerobic biodegradability. For co-digestion trials, the highest values were reached for pretreatment at 120 °C for 60 min, which led to 196 mLCH4/gVS and maximum methane production rate of 0.38 d-1.

Physical Pretreatment Methods for Improving Microalgae Anaerobic Biodegradability.

Microalgae may be a potential feedstock for biogas production through anaerobic digestion. However, this process is limited by the hydrolytic stage, due to the complex and resistant microalgae cell wall components. This fact hinders biomass conversion into biogas, demanding the application of pretreatment techniques for inducing cell damage and/or lysis and organic matter solubilisation. In this study, sonication, thermal, ultrasound, homogeneizer, hydrothermal and steam explosion pretreatments were evaluated in different conditions for comparing their effects on anaerobic digestion performance in batch reactors. The results showed that the highest biomass solubilisation values were reached for steam explosion (65-73%) and ultrasound (33-57%). In fact, only applied energies higher than 220 W or temperatures higher than 80 °C induced cell wall lysis in C. sorokiniana. Nonetheless, the highest methane yields were not correlated to biogas production. Thermal hydrolysis and steam explosion showed lower methane yields in respect to non-pretreated biomass, suggesting the presence of toxic compounds that inhibited the biological process. Accordingly, these pretreatment techniques led to a negative energy balance. The best pretreatment method among the ones evaluated was thermal pretreatment, with four times more energy produced that demanded.

Steam explosion pretreatment improved the biomethanization of coffee husks.

This study evaluated the potential of energy generation using a combined heat and power co-generation system (CHP) from biogas produced during the anaerobic digestion of coffee husks (CH) pretreated with steam explosion. Pretreatment conditions assessed were time (1, 5, 15 and 60min) and temperature (120, 180 and 210°C). Polysaccharides solubilisation and biogas production were not correlated. While pretreatment with severities higher than 4 resulted in a highest solubilisation of cellulose, hemicelluloses and lignin; however, furans concentration in those cases hindered biomass biodegradation. Considering a CHP, all pretreatment conditions were worthwhile when compared to non-pretreated CH. The best condition was 120°C for 60min, in which a 2.37 severity showed the highest methane yield (144.96NmLCH4gCOD-1) and electricity production (0.59kWhkgCH-1). However, even better results could be achieved using 120°C for only 5min, which would lead to a larger amount of CH daily processed.

Anaerobic digestion of hemicellulose hydrolysate produced after hydrothermal pretreatment of sugarcane bagasse in UASB reactor.

In the context of a sugarcane biorefinery, sugarcane bagasse produced may be pretreated generating a solid and liquid fraction. The solid fraction may be used for 2G bioethanol production, while the liquid fraction may be used to produce biogas through anaerobic digestion. The aim of this study consisted in evaluating the anaerobic digestion performance of hemicellulose hydrolysate produced after hydrothermal pretreatment of sugarcane bagasse. For this, hydrothermal pretreatment was assessed in a continuous upflow anaerobic sludge blanket (UASB) reactor operated at a hydraulic retention time (HRT) of 18.4h. Process performance was investigated by varying the dilution of sugarcane bagasse hydrolysate with a solution containing xylose and the inlet organic loading rate (OLR). Experimental data showed that an increase in the proportion of hydrolysate in the feed resulted in better process performance for steps using 50% and 100% of real substrate. The best performance condition was achieved when increasing the organic loading rate (OLR) from 1.2 to 2.4gCOD/L·d, with an organic matter removal of 85.7%. During this period, the methane yield estimated by the COD removal would be 270LCH4/kg COD. Nonetheless, when further increasing the OLR to 4.8gCOD/L·d, the COD removal decreased to 74%, together with an increase in effluent concentrations of VFA (0.80gCOD/L) and furans (115.3mg/L), which might have inhibited the process performance. On the whole, the results showed that anaerobic digestion of sugarcane bagasse hydrolysate was feasible and may improve the net energy generation in a bioethanol plant, while enabling utilization of the surplus sugarcane bagasse in a sustainable manner.

Thermochemical pretreatment and anaerobic digestion of dairy cow manure: Experimental and economic evaluation.

The aim of this study was to assess technically and economically the application thermochemical pretreatment in the anaerobic digestion of dairy cow manure. After selecting the optimum substrate to inoculum (S/I) ratio in a preliminary BMP test, the following tests compared 20 different pretreatment conditions varying temperature (100 and 37°C), exposure time (5 and 30min and 12 and 24h) and chemical doses (0.5, 2, 6 and 10% of HCl or NaOH). The highest value of maximum production rate was achieved at an S/I ratio of 0.25gVSsgVSi-1. The major improvements of the methane potential were 23.6% with 10% of NaOH at 100°C for 5min and 20.6% with 2% of HCl at 37°C. The technical-economic analysis showed that the implementation of neither thermal alkali nor thermal-acid pretreatment would be feasible and the conventional one-step anaerobic digestion outperforms both alternatives.

Reuse of microalgae grown in full-scale wastewater treatment ponds: Thermochemical pretreatment and biogas production.

This study assessed thermochemical pretreatment of microalgae harvested from a full-scale wastewater treatment pond prior to its anaerobic digestion using acid and alkaline chemical doses combined with thermal pretreatment at 80°C. Results indicated that alkaline and thermal pretreatment contributed mostly to glycoprotein and pectin solubilisation; whilst acid pretreatment solubilised mostly hemicellulose, with lower effectiveness for proteins. Regarding the anaerobic biodegradability, biochemical methane potential (BMP) tests showed that final methane yield was enhanced after almost all pretreatment conditions when compared to non-pretreated microalgae, with the highest increase for thermochemical pretreatment at the lowest dose (0.5%), i.e. 82% and 86% increase for alkaline and acid, respectively. At higher doses, salt toxicity was revealed by K(+) concentrations over 5000mg/L. All BMP data from pretreated biomass was successfully described by the modified Gompertz model and optimal condition (thermochemical 0.5% HCl) showed an increase in final methane yield and the process kinetics.