Hybrid anion exchanger for trace phosphate removal from water and wastewater

Throughout recent decades, the wastewater treatment industry has identified the discharge of nutrients, including phosphates and nitrates, into waterways as a risk to natural environments due to the serious effects of eutrophication. For this reason, new tertiary treatment processes have abounded; these processes generally utilize physico-chemical and biological methods to remove nutrients from secondary wastewaters. The disadvantages of such methods involve larger reactor volumes, operating costs, and waste sludge production; furthermore, complete nutrient removal is unattainable due to thermodynamic and kinetic limitations. The subject study presents the development and performance of a new phosphate-selective sorbent, referred to as hybrid anion exchanger or HAIX. HAIX combines durability and mechanical strength of polymeric anion exchange resins with high sorption affinity of hydrated ferric oxide (HFO) toward phosphate. HAIX is essentially a polymeric anion exchanger within which HFO nanoparticles have been dispersed irreversibly. Laboratory studies show that HAIX selectively removes phosphate from the background of much higher concentrations of competing sulfate, chloride and bicarbonate anions due to the combined presence of Coulombic and Lewis acid-base interactions. Experimental results demonstrate that HAIX's phosphate-sulfate separation factor is over two orders of magnitude greater than that of currently available commercial ion exchange resins. Additionally, optimal HAIX performance occurs at typical secondary wastewater pH conditions i.e., around 7.5. HAIX is amenable to efficient regeneration and reuse with no noticeable loss in capacity.     

Development of an innovative vertical submerged membrane bioreactor (VSMBR) for simultaneous removal of organic matter and nutrients

A novel vertical submerged membrane bioreactor (VSMBR) composed of anoxic and oxic zones in one reactor was developed in an attempt to reduce the problems concerning effective removal of pollutants from synthetic wastewater including glucose as a sole carbon source as well as membrane fouling. The optimal volume ratio of anoxic zone/oxic zone was found as 0.6. The desirable internal recycle rate and hydraulic retention time (HRT) for effective nutrient removal were 400% and 8h, respectively. Under these conditions, the average removal efficiencies of total nitrogen (T-N) and total phosphorus (T-P) were 75% and 71%, respectively, at the total chemical oxygen demand (T-COD)/T-N ratio of 10. In addition, the VSMBR showed high specific removal rates of nitrogen and phosphorus while the biomass growth yield from the reactor was about 20% of the conventional activated sludge process.     

Baffled membrane bioreactor (BMBR) for efficient nutrient removal from municipal wastewater

Submerged membrane bioreactors (MBRs) are now widely used for various types of wastewater treatment. One drawback of submerged MBRs is the difficulty in removing nitrogen because intensive aeration is usually carried out in the tank and the MBRs must therefore be operated under aerobic conditions. In this study, the feasibility of treating municipal wastewater by a baffled membrane bioreactor (BMBR), particularly in terms of nitrogen removal, was examined. Simultaneous nitrification/denitrification in a single and small reaction tank was possible by inserting baffles into a normal submerged MBR as long as wastewater was fed in the appropriate way. To examine the applicability of the BMBR, pilot-scale experiments were carried out using real municipal wastewater. Although neither external carbon addition nor mixed liquor circulation was carried out in the operation of the BMBR, average removal rates of total organic carbon (TOC), total phosphorus (T-P) and total nitrogen (T-N) reached 85%, 97% and 77%, respectively, with the hydraulic retention time (HRT) of 4.7h. Permeability of the membrane could be maintained at a high level throughout the operation. It was found that denitrification was the limiting step in removal of nitrogen in the BMBR in this study. Various types of monitoring carried out in the BMBR also demonstrated the possibility of further improvements in its performance.     

Driving factors of the phytoplankton functional groups in a deep Mediterranean reservoir

The control of phytoplankton growth is mainly related to the availability of light and nutrients. Both may select phytoplankton species, but only if they occur in limiting amounts. During the last decade, the functional groups approach, based on the physiological, morphological and ecological attributes of the species, has proved to be a more efficient way to analyze seasonal changes in phytoplankton biomass. We analysed the dynamics of the phytoplankton functional groups sensu Reynolds, recognising the driving forces (light, mixing regime, and nutrients) in the Sau Reservoir, based on a one-year cycle (monthly surface-water sampling). The Sau Reservoir is a Mediterranean water-supply reservoir with a canyon-shaped basin and a clear and mixed epilimnion layer. The long stratification period and high light availability led to high phytoplankton biomass (110.8 fresh-weight mg L⁻¹) in the epilimnion during summer. The reservoir showed P-limitation for phytoplankton growth in this period. All functional groups included one or more species (X2-Rhodomonas spp.; Y-Cryptomonas spp.; F-Oocystis lacustris; K-Aphanocapsa spp.) selected by resources, especially phosphorus. Species of Cryptomonas (group Y) dominated during the mixing period (winter season) in conditions of low light and relatively high availability of dissolved nutrients. Increases in water-column stability during spring stratification led to phytoplankton biomass increases due to the dominance of small flagellate functional groups (X2 and X3, chrysophyceans). The colonial chlorophycean O. lacustris (group F) peaked during the mid-summer stratification, when the mixed epilimnion was clearly depleted in nutrients, especially SRP. High temperature and increases in nutrient concentration during the end-summer and mid-autumn resulted in a decrease of green algae (group F) and increase of Aphanocapsa spp. (cyanobacteria, group K) and dinoflagellates (group L_o). The study also revealed the important role of physical processes in the seasonal gradient, in selecting phytoplankton functional groups, and consequently in the assessment of ecological status. The Q index (assemblage index) based on functional groups indicated the overall good ecological status of the Sau Reservoir, which varied as a function of the mixing regime. This is the first application of the Assemblage Index to a European water-supply reservoir.     

Reducing the startup time of aerobic granular sludge reactors through seeding floccular sludge with crushed aerobic granules

One of the main challenging issues for the aerobic granular sludge technology is the long startup time when dealing with real wastewaters. This study presents a novel strategy to reduce the time required for granulation while ensuring a high level of nutrient removal. This new approach consists of seeding the reactor with a mixture of crushed aerobic granules and floccular sludge. The effectiveness of the strategy was demonstrated using abattoir wastewater, containing nitrogen and phosphorus at approximately 250 mgN/L and 30 mgP/L, respectively. Seven different mixtures of crushed granules and floccular sludge at granular sludge fractions (w/w in dry mass) of 0%, 5%, 10%, 15%, 25%, 30% and 50% were used to start eight granulation processes. The granulation time (defined as the time when the 10th percentile bacterial aggregate size is larger than 200 μm) displayed a strong dependency on the fraction of granular sludge. The shortest granulation time of 18 days was obtained with 50% crushed granules, in comparison with 133 days with 5% crushed granules. Full granulation was not achieved in the two trials without seeding with crushed granules. In contrast to the 100% floccular sludge cases, where a substantial loss of biomass occurred during granulation, the biomass concentration in all other trails did not decrease during granulation. This allowed that good nitrogen removal was maintained in all the reactors during the granulation process. However, enhanced biological phosphorus removal was achieved in only one of the eight trials. This was likely due to the temporary accumulation of nitrite, a strong inhibitor of polyphosphate accumulating organisms.     

The behaviour of pharmaceuticals and heavy metals during struvite precipitation in urine

Separating urine from wastewater at the source reduces the costs of extensive wastewater treatment. Recovering the nutrients from urine and reusing them for agricultural purposes adds resource saving to the benefits. Phosphate can be recovered in the form of struvite (magnesium ammonium phosphate). In this paper, the behaviour of pharmaceuticals and heavy metals during the precipitation of struvite in urine is studied.When precipitating struvite in urine spiked with hormones and non-ionic, acidic and basic pharmaceuticals, the hormones and pharmaceuticals remain in solution for more than 98%.For heavy metals, initial experiments were performed to study metal solubility in urine. Solubility is shown to be affected by the chemical conditions of stored and therefore hydrolysed urine. Thermodynamic modelling reveals low or very low equilibrium solute concentrations for cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni) and lead (Pb). Experiments confirmed Cd, Cu and Pb carbonate and hydroxide precipitation upon metal addition in stored urine with a reaction half-life of ca. 7 days.For all metals considered, the maximum specific metal concentrations per gram phosphate or nitrogen showed to be typically several orders of magnitudes lower in urine than in commercially available fertilizers and manure. Heavy metals in struvite precipitated from normal stored urine could not be detected.Phosphate recovery from urine over struvite precipitation is shown to render a product free from most organic micropollutants and containing only a fraction of the already low amounts of heavy metals in urine.     

Biomass yield,nitrogen response,and nutrient uptake of perennial bioenergy grasses in North Carolina

Although perennial grasses show considerable potential as candidates for lignocellulosic bioenergy production, these crops exhibit considerable variation in regional adaptability and yield. Giant miscanthus (Miscanthus × giganteus Greef & Deuter), Miscanthus sinensis Anderss. ‘Gracillimus’ and MH2006, plume grass (Saccharum arundinaceum Retz.), ravenna grass (Saccharum ravennae (L.) L.), switchgrass (Panicum virgatum L. ‘Alamo’), and giant reed (Arundo donax L.) field plots were established in 2008, treated with four nitrogen (N) fertilizer rates (0, 34, 67, 134 kg ha⁻¹ y⁻¹), and harvested annually in winter from 2008 to 2011. Giant reed, ‘Gracillimus’, switchgrass, MH2006, giant miscanthus and ravenna grass at the Mountain site produced mean dry matter yields of 22.8, 21.3, 20.9, 19.3, 18.4, and 10.0 Mg ha⁻¹ y−¹, respectively (averaged over the last two years). Dry matter yields at the Coastal site for giant reed, giant miscanthus, switchgrass, ravenna grass, and ‘Gracillimus’ were 27.4, 20.8, 20.1, 14.3, and 9.4 Mg ha⁻¹ y⁻¹, respectively (averaged over the last two years). Increasing N rates up to 134 kg N ha⁻¹ did not have a consistent significant effect on biomass production. High yields coupled with high mortality for plume grass at both sites indicates its potential as a bioenergy crop and need for continued improvement. Overall, the perennial grasses in this study had low nutrient removal, although giant reed and plume grass often removed significantly more N, P, K and S compared with Miscanthus spp. and switchgrass. Our results indicate that giant reed, giant miscanthus, and switchgrass are productive bioenergy crops across geographic regions of North Carolina.     

Development of a knowledge library for automated watershed modeling

In this work, we develop a library of components for building semi-distributed watershed models. The library incorporates basic modeling knowledge that allows us to adequately model different water fluxes and nutrient loadings on a watershed scale. It is written in a formalism compliant with the equation discovery tool ProBMoT, which can automatically construct watershed models from the components in the library, given a conceptual model specification and measured data. We apply the proposed modeling methodology to the Ribeira da Foupana catchment to extract a set of viable hydrological models. By specifying the conceptual model and using the knowledge library, two different hydrological models are generated. Both models are automatically calibrated against measurements and the model with the lower root mean squared error (RMSE) value is selected as an appropriate hydrological model for the selected study area.     

Substratum attachment location and biofilm formation by Bacillus cereus strains isolated from different sources: Effect on total biomass production and sporulation in different growth conditions

Bacillus cereus, an endospore forming human pathogen associated with foodborne diseases, can form biofilms and attach to surfaces of processing equipment in the food industry. It is a consistent source of contamination and/or cross contamination of processed food products. The objective of this study was to understand substratum attachment location and biofilm formation behavior of B. cereus strains under different growth conditions. A total of 60 strains isolated from food, human, or farm and a number of reference strains were used in this study. Substratum attachment locations of these strains in 96-well microtiter plates were highly diversified among these strains. Strains isolated from food showed higher preference to attach at the air-liquid interface during early stage of biofilm formation. To the best of our knowledge, this is the first report showing the level of substratum attachment location and biofilm formation of B. cereus strains isolated from different sources. Substratum properties did not affect biofilm formation location when a number of selected strains were grown on stainless steel coupon, indicating that biofilm formation location might be independent of the type of substratum. Substratum attachment location and biofilm formation related phenotypes such as total biomass production, number of sessile cells, and sporulation were closely correlated. Substratum attachment location and sporulation behavior were strongly affected during biofilm formation under nutrient stress condition. The number of spores was significantly increased in biofilms grown under nutrient stress condition even though total biomass formation was lower. Our results on substratum attachment location and related biofilm formation behavior are substantially important for food industries where different surfaces are prone to B. cereus attachment, particularly for setting up and implementing clean in place (CIP) protocols.     

Effects of N/C,P/C and Fe/C ratios on dark fermentative hydrogen gas production from waste paper towel hydrolysate

The effects of N/C, P/C and Fe/C ratios on dark fermentative hydrogen gas production from activated carbon treated WPT hydrolysate were investigated using Box–Behnken statistical experiment design. N/C, P/C and Fe/C ratios were chosen as independent variables while the H₂ yield and SHPR were set as the objective functions. H₂ yield and SHPR functions were described by two quadratic model functions. The addition of a proper amount of N, P and Fe to the fermentation media was found to be essential to enhance the H₂ production performance. Linear and interaction terms of N/C and Fe/C did have a significant effect on the H₂ yield in the model function. However, the SHPR was significantly affected by the linear and interaction terms of N/C and P/C. The most convenient N/C, P/C and Fe/C ratios resulting maximum H₂ yield (0.656 mol H₂/mol glucose) and SHPR (241.64 mL H₂/g biomass.h) were determined as 0.05, 0.09 and 0.003 (w/w), respectively.