Polyhydroxyalkanoates production in purple phototrophic bacteria ponds: A breakthrough in outdoor pilot-scale operation.

The versatile capacity of purple phototrophic bacteria (PPB) for producing valuable bioproducts has gathered renewed interest in the field of resource recovery and waste valorisation. However, greater knowledge regarding the viability of applying PPB technologies in outdoor, large-scale systems is required. This study assessed, for the first time, the upscaling of the phototrophic polyhydroxyalkanoate (PHA) production technology in a pilot-scale system operated in outdoor conditions. An integrated system composed of two up-flow anaerobic sludge blanket (UASB) reactors (for fermentation of wastewater with molasses), and two high-rate algal ponds retrofitted into PPB ponds, was operated in a wastewater treatment plant under outdoor conditions. UASB's adaptation to the outdoor temperatures involved testing different operational settings, namely hydraulic retention times (HRT) of 48 and 72 h, and molasses fermentation in one or two UASBs. Results have shown that the fermentation of molasses in both UASBs with an increased HRT of 72 h was able to ensure a suitable operation during colder conditions, achieving 3.83 ± 0.63 g CODFermentative Products/L, compared to the 3.73 ± 0.85 g CODFermentative Products/L achieved during warmer conditions (molasses fermentation in one UASB; HRT 48 h). Furthermore, the PPB ponds were operated under a light-feast/dark-aerated-famine strategy and fed with the fermented wastewater and molasses from the two UASBs. The best PHA production was obtained during the summer of 2018 and spring of 2019, attaining 34.7 % gPHA/gVSS with a productivity of 0.11 gPHA L-1 day-1 and 36 % gPHA/gVSS with a productivity of 0.14 gPHA L-1 day-1, respectively. Overall, this study showcases the first translation of phototrophic PHA production technology from an artificially illuminated laboratory scale system into a naturally illuminated, outdoor, pilot-scale system. It also addresses relevant process integration aspects with UASBs for pre-fermenting wastewater with molasses, providing a novel operational strategy to achieve photosynthetic PHA production in outdoor full-scale systems.

Membrane-based pretreatment to mitigate variations in desalination plants.

The main source of potable water in high water-stress areas is commonly produced in brackish and seawater desalination plants. Owing to the presence of high concentration of suspended solids, organic matter and colloidal particles in raw water, pretreatment processes are needed for a stable operation of desalination plants. A submerged membrane ultrafiltration pilot plant has been operated as pretreatment of complex brackish surface water to study the filtration performance. The results show the membrane performance, chemical reagent requirements, water quality and cleaning procedures efficiency of an ultrafiltration pilot plant used as pretreatment for a reverse osmosis system. Alternative chemical cleaning procedures have been satisfactorily implemented, which maximize permeability recovery and allow a stable operation.

Evaluation of High Rate Algae Ponds for treatment of anaerobically digested wastewater: Effect of CO2 addition and modification of dilution rate.

High Rate Algae Ponds (HRAP) are the simplest way to grow microalgae biomass and an interesting alternative for wastewater treatment. In this work the performance of these systems was evaluated using anaerobically digested wastewater as culture medium. Two variables were studied in long-term mode: the carbon dioxide supply and the modification of the dilution rates. The results showed that CO2 supply increases the productivity but less than expected considering the potential biomass generation calculated based on the ratios of carbon to nitrogen of microalgae and wastewater. The assimilation into biomass only accounted for 57% of the inlet nitrogen under the best conditions because nitrification and volatilization reduced the availability of this element. The operation under short hydraulic retention times presented a more interesting performance with higher biomass productivities. The biomass produced was efficiently harvested with in a Dissolved Air Flotation (DAF) unit.

Influence of dissolved oxygen concentration on the start-up of the anammox-based process: ELAN®.

The anammox-based process ELAN® was started-up in two different sequencing batch reactor (SBR) pilot plant reactors treating municipal anaerobic digester supernatant. The main difference in the operation of both reactors was the dissolved oxygen (DO) concentration in the bulk liquid. SBR-1 was started at a DO value of 0.4 mg O2/L whereas SBR-2 was started at DO values of 3.0 mg O2/L. Despite both reactors working at a nitrogen removal rate of around 0.6 g N/(L d), in SBR-1, granules represented only a small fraction of the total biomass and reached a diameter of 1.1 mm after 7 months of operation, while in SBR-2 the biomass was mainly composed of granules with an average diameter of 3.2 mm after the same operational period. Oxygen microelectrode profiling revealed that granules from SBR-2 where only fully penetrated by oxygen with DO concentrations of 8 mg O2/L while granules from SBR-1 were already oxygen penetrated at DO concentrations of 1 mg O2/L. In this way granules from SBR-2 performed better due to the thick layer of ammonia oxidizing bacteria, which accounted for up to 20% of all the microbial populations, which protected the anammox bacteria from non-suitable liquid media conditions.

Implications of full-scale implementation of an anammox-based process as post-treatment of a municipal anaerobic sludge digester operated with co-digestion.

The feasibility of treating the supernatant of a municipal sludge digester supplemented with co-substrates by means of an anammox-based process (ELAN(®)) was tested in Guillarei (NW of Spain). Ammonia concentration measured in the supernatant of the sludge digester varied in the range 800-1,500 g N/m(3) due to the fact that the sludge produced in the plant was co-digested with wastes coming from surrounding food industries. Treating this supernatant in the ELAN(®) reactor, nitrogen removal rates up to 1.1 kg N/(m(3) d) were reached in experiments run in a pilot plant reactor operated in batch mode. No nitrite oxidation was registered after several months of operation despite the average dissolved oxygen (DO) concentrations being 1.5 g O2/m(3) and the temperature reaching values as low as 18 °C. By keeping the DO set point at 1-2 g O2/m(3) and tuning the hydraulic retention time, the stability of the process was guaranteed and the presence of co-substrates in the anaerobic digester did not affect negatively the operation of the autotrophic nitrogen removal process. Due to the success of the pilot plant experiment, an upscale of the process to full scale is proposed. Mass balances applied to Guillarei wastewater treatment plant revealed that in the main stream line the average denitrification rate calculated with the data of year 2011 was 226 kg N/d. Since the nitrogen removal efficiency is limited by the amount of readily biodegradable organic matter available to carry out denitrification in the water line, the implementation of an anammox-based process to treat the supernatant seems the best option to improve the effluent quality in terms of nitrogen content. The nitrogen removal rate in the sludge line would be 30 times higher than the one in the water line. The implementation of the process would improve the energetic balance and the nitrogen removal performance of the plant.

Evaluation of carbon dioxide mass transfer in raceway reactors for microalgae culture using flue gases.

Mass transfer of CO2 from flue gas was quantified in a 100m(2) raceway. The carbonation sump was operated with and without a baffle at different liquid/gas ratios, with the latter having the greatest influence on CO2 recovery from the flue gas. A rate of mass transfer sufficient to meet the demands of an actively growing algal culture was best achieved by maintaining pH at ∼8. Full optimisation of the process required both pH control and selection of the best liquid/gas flow ratio. A carbon transfer rate of 10gCmin(-1) supporting an algal productivity of 17gm(-2)day(-1) was achieved with only 4% direct loss of CO2 in the sump. 66% of the carbon was incorporated into biomass, while 6% was lost by outgassing and the remainder as dissolved carbon in the liquid phase. Use of a sump baffle required additional power without significantly improving carbon mass transfer.

Biochemical methane potential of microalgae: influence of substrate to inoculum ratio, biomass concentration and pretreatment.

The anaerobic digestion of three microalgae mixtures was evaluated at different substrate to inoculum (S/I) ratios (0.5, 1 and 3), biomass concentrations (3, 10 and 20gTS/kg) and pretreatments (thermal hydrolysis, ultrasound and biological treatment). An S/I ratio of 0.5 and 10gTS/kg resulted in the highest final methane productivities regardless of the microalgae tested (ranging from 188 to 395mL CH(4)/gVS(added)). The biological pretreatment supported negligible enhancements on CH(4) productivity, while the highest increase (46-62%) was achieved for the thermal hydrolysis. The optimum temperature of this pretreatment depended on the microalgae species. The ultrasound pretreatment brought about increases in CH(4) productivity ranging from 6% to 24% at 10,000kJ/kgTS, without further increases at higher energy inputs. The results here obtained confirmed the lack of correlation between the solubilization degree and the methane enhancement potential and pointed out that anaerobic digestion of algae after thermal pretreatment is a promising technology for renewable energy production.

Comparing cost and process performance of activated sludge (AS) and biological aerated filters (BAF) over ten years of full sale operation.

In the early 1990s, the Wastewater Treatment Plant (WWTP) of Frederikshavn, Denmark, was extended to meet new requirements for nutrient removal (8 mg/L TN, 1.5 mg TP/L) as well as to increase its average daily flow to 16,500 m(3)/d (4.5 MGD). As the most economical upgrade of the existing activated sludge (AS) plant, a parallel biological aerated filter (BAF) was selected, and started up in 1995. Running two full scale processes in parallel for over ten years on the same wastewater and treatment objectives enabled a direct comparison in relation to operating performance, costs and experience. Common pretreatment consists of screening, an aerated grit and grease removal and three primary settlers with chemical addition. The effluent is then pumped to the two parallel biological treatment stages, AS with recirculation and an upflow BAF with floating media. The wastewater is a mixture of industrial and domestic wastewater, with a dominant discharge of fish processing effluent which can amount to 50% of the flow. The maximum hydraulic load on the pretreatment section as a whole is 1,530 m(3)/h. Approximately 60% of the sewer system is combined with a total of 32 overflow structures. To avoid the direct discharge of combined sewer overflows into the receiving waters, the total hydraulic wet weather capacity of the plant is increased to 4,330 m(3)/h, or 6 times average flow. During rain, some of the raw sewage can be directed through a stormwater bypass to the BAF, which can be modified in its operation to accommodate various treatment needs: either using simultaneous nitrification/denitrification in all filters with recirculation introducing bottom aeration with full nitrification in some filters for storm treatment and/or post-denitrification in one filter. After treatment, the wastewater is discharged to the Baltic Sea through a 500 m outfall. The BAF backwash sludge, approximately 1,900 m(3) per 24 h in dry weather, is redirected to the AS plant. Primary settler sludge and the combined biosolids from the AS plant are anaerobically digested, with methane gas being used for generation of heat and power. On-line measurements for the parameters NO3, NO2, NH4, temperature as well as dissolved oxygen (DO) are used for control of aeration and external carbon source (methanol). Dosing of flocculants for P-removal is carried out based on laboratory analysis and jar tests. This paper discusses the experience gained from the plant operation during the last ten years, compiling comparative performance and cost data of the two processes, as well as their optimisation.

Fixed film phosphorus removal--flexible enough?

While biological phosphorus removal (BPR) has been practised for 30 years, up to recently it has been restricted mainly to activated sludge processes, with the corresponding need for large basin volumes. Yet, research with biofilm reactors showed that the principle of alternate anaerobic and aerated conditions was applicable to fixed bacteria by changing the conditions in time rather than in space. Attached growth enhanced biological phosphorus removal (EBPR) systems are attractive because of their compactness and capability to retain high biomass levels. However, the phosphorus extraction depends on backwashes to enhance the phosphorus-rich attached biomass, and correct control of unsteady effluent quality created by frequently modified process conditions. Accordingly, EBPR remains a challenging task in terms of combining nitrogen and phosphorus removal using attached growth systems. Nevertheless, a combination of activated sludge and biofilm carriers, in the integrated fixed-film activated sludge system, provides treatment opportunities not readily available using suspended growth systems. Current practice is only at the beginning of exploiting the full potential of this combination, but the first full-scale results show that compact tankage and low nutrient results based on biological principles are possible.

MELISSA: a potential experiment for a precursor mission to the Moon.

MELISSA (Micro-Ecological Life Support System Alternative) has been conceived as a micro-organism based ecosystem intended as a tool for developing the technology for a future artificial ecosystem for long term space missions, as for example a lunar base. The driving element of MELISSA is the recovering of edible biomass from waste, CO2, and minerals with the use of sun light as energy source. In this publication, we focus our attention on the potential applications of MELISSA for a precursor mission to the Moon. We begin by a short review of the requirements for bioregenerative Life Support. We recall the concept of MELISSA and the theoretical and technical approaches of the study. We present the main results obtained since the beginning of this activity and taking into account the requirements of a mission to the Moon we propose a preliminary experiment based on the C cycle of the MELISSA loop.