Enhanced Ammonia Removal Research Articles

Innovative Juncus effusus plant biofilter for enhanced ammonia removal: design, construction, and preliminary testing

A developing trend in stormwater treatment and management is the use of green technologies. Plant biofilters have been gaining increasing use in support of green technology objectives. This technical note reports on the development and preliminary testing of a laboratory-scale plant biofilter prototype for ammonia removal using a South African native plant species (Juncus effusus). The prototype design was based on a conceptual model for nitrogen fixation, plant uptake, bacterial nitrification and soil sorption. Additionally, a plug compartment was incorporated into the design to simulate plug flow as part of the conceptual model. Biofilter models with and without inoculated bacteria were compared. Ammonia reduction, nitrite and nitrate formation were observed. Results showed that the inoculated plant biofilter performed best, with an average of 61% reduction in ammonia within the filter compared to 15% in the normal plant biofilter. The incorporation of a plug compartment aided in slowing down the ammonia infiltration rate, increasing the retention time, and allowing for nitrification to occur.

Enhanced ammonia removal in tidal flow constructed wetland by incorporating steel slag: Performance, microbial community, and heavy metal release

Utilizing alkaline solid wastes, such as steel slag, as substrates in tidal flow constructed wetlands (TFCWs) can effectively neutralize the acidity generated by nitrification. However, the impacts of steel slag on microbial communities and the potential risk of heavy metal release remain poorly understood. To address these knowledge gaps, this study compared the performance and microbial community structure of TFCWs filled with a mixture of steel slag and zeolite (TFCW-S) to those filled with zeolite alone (TFCW-Z). TFCW-S exhibited a much higher NH4+-N removal efficiency (98.35 %) than TFCW-Z (55.26 %). Additionally, TFCW-S also achieved better TN and TP removal. The steel slag addition helped maintain the TFCW-S effluent pH at around 7.5, while the TFCW-Z effluent pH varied from 3.74 to 6.25. The nitrification and denitrification intensities in TFCW-S substrates were significantly higher than those in TFCW-Z, consistent with the observed removal performance. Moreover, steel slag did not cause excessive heavy metal release, as the effluent concentrations were below the standard limits. Microbial community analysis revealed that ammonia-oxidizing bacteria, ammonia-oxidizing archaea, and complete ammonia-oxidizing bacteria coexisted in both TFCWs, albeit with different compositions. Furthermore, the enrichment of heterotrophic nitrification-aerobic denitrification bacteria in TFCW-S likely contributed to the high NH4+-N removal. In summary, these findings demonstrate that the combined use of steel slag and zeolite in TFCWs creates favorable pH conditions for ammonia-oxidizing microorganisms, leading to efficient ammonia removal in an environmentally friendly manner.

Low-concentration organics mitigate the inhibition of free nitrous acid on nitrification in biofilters for gaseous ammonia removal

The accumulation of free nitrous acid (FNA), a by-product of nitritation, restricts biofilter ammonia removal under medium-to-high inlet ammonia loading by inhibiting nitrifiers. Preliminarily testing under varying C/N ratios validated that the addition of low-concentration organics carbon (OC, C/N = 1.0–1.5) effectively alleviated FNA accumulation, thereby improving biofilter performance. Subsequently, three parallel ammonia removal biofilters with different inocula were set to investigate the underlying mechanisms. Upon elevating the inlet ammonia loading rate to 22.8 ± 1.2 gN m–3h−1, the biofilters removed only 60.3 ± 10.0 % of gaseous ammonia under inorganic carbon (IC) supplementation. However, the introduction of low-concentration OC (C/N = 1.0) facilitated nitrogen loss, enriched denitrifying bacteria (DNB), and bolstered the denitrification functional abundance. The successful coupling of denitrification significantly reduced FNA concentrations by 2 to 3 orders of magnitude. Therefore, the revival of nitrifiers contributed to the enhanced ammonia removal efficiency (94.2 ± 8.4 %). Nitrite-oxidizing bacteria (NOB) and DNB subcommunities were identified as the driving factors for the mitigation of FNA and improvement of biofilter performance by the Mantel test. Activated heterotrophs facilitated ammonia conversion as well when OC was supplied, supported by Pearson correlation analysis. This study elucidated the synergistic dynamics between nitrifiers and DNB, emphasizing the favorable cooperation arising from the low-concentration OC addition (C/N = 1.0–1.5). Overall, this study highlights the cooperative interaction between heterotrophic denitrifiers and autotrophic nitrifiers under low-concentration OC supply, which played a vital role in alleviating FNA inhibition and enhancing the biofilter ammonia removal efficiency.

MOF incorporated adsorptive nanofibrous membranes for enhanced ammonia removal by membrane distillation

This study presents the design and fabrication of a new adsorptive nanofibrous membrane incorporating metal-organic framework (MOF) by electrospinning technique for removing ammonia-nitrogen from wastewater via direct contact membrane distillation (DCMD) process. Three types of MOF particles (HKUST-1, AlFu, and UiO-66-NH2) were used as functional nanoadditives and incorporated into the nanofibrous membrane matrix. The ammonia removal performance of these nanocomposite membranes was comprehensively investigated and compared with an activated carbon (AC) incorporated nanofibrous membrane. Various parameters such as ammonia removal efficiency, ammonia separation factor, overall ammonia mass transfer coefficient, ammonia flux, and membrane stability were evaluated. Among the tested MOFs, UiO-66-NH2 demonstrated excellent performance and was selected for further optimization. The 5.0 wt.% UiO-66-NH2 incorporated membrane exhibited the best performance for ammonia removal. Additionally, the mechanism of MOF incorporated nanofibrous membranes for ammonia removal from aqueous solution by DCMD was schematically analyzed. In overall, this study confirmed the feasibility of fabricating MOF incorporated electrospun adsorptive nanofibrous membranes with outstanding ammonia removal performance, demonstrating the potential of membrane distillation to remove ammonia-nitrogen from the aquatic environment.

Enhanced ammonia removal from skim latex using air bubbles in an agitated column

AbstractThe initial aim of the paper is to improve the ammonia removal efficiency from skim latex using air stripping in an agitated column. The effects of air flow rate, bubble sizes, types of impellers, and rotational speed were investigated. The results showed that ammonia decreased with the increased air flow rate and the decreased bubble size. More ammonia could be removed by the use of impellers at a low rotational speed. The axial flow impeller showed higher ammonia removal than that gained from the radial flow impeller. It could be concluded that the stripping process in an agitated column should be operated at an air flow rate under the homogeneous regime without pH and temperature adjustment. The use of axial flow impeller at a rotational speed below the turbulent flow is recommended for more ammonia removal. In addition, smaller bubbles than the working range proposed in this research should be avoided because of foaming formation of the skim latex.

An enriched ammonia-oxidizing microbiota enables high removal efficiency of ammonia in antibiotic production wastewater

High ammonia concentration hinders the efficient treatment of antibiotic production wastewater (APW). Developing effective ammonia oxidation wastewater treatment strategies is an ideal approach for facilitating APW treatment. Compared with traditional nitrification strategies, the partial nitrification process is more eco-friendly, less energy-intensive, and less excess sludge. The primary limiting factor of the partial nitrification process is increasing ammonia-oxidizing bacteria (AOB) while decreasing nitrite-oxidizing bacteria (NOB). In this study, an efficient AOB microbiota (named AF2) was obtained via enrichment of an aerobic activated sludge (AS0) collected from a pharmaceutical wastewater treatment plant. After a 52-day enrichment of AS0 in 250 mL flasks, the microbiota AE1 with 69.18% Nitrosomonas microorganisms was obtained. Subsequent scaled-up cultivation in a 10 L fermenter led to the AF2 microbiota with 59.22% Nitrosomonas. Low concentration of free ammonia (FA, < 42.01 mg L−1) had a negligible effect on the activity of AF2, and the nitrite-nitrogen accumulation rate (NAR) of AF2 was 98% when FA concentration was 42.01 mg L−1. The specific ammonia oxidation rates (SAORs) at 30 °C and 15 °C were 3.64 kg NH4+-N·kg MLVSS−1·d−1 and 1.43 kg NH4+-N·kg MLVSS−1·d−1 (MLVSS: mixed liquor volatile suspended solids). The SAOR was 0.52 kg NH4+-N·kg MLVSS−1·d−1 when the NaCl concentration was increased from 0 to 20 g L−1, showing that AF2 functioning was stable in a high-level salt environment. The ammonia oxidation performance of AF2 was verified by treating abamectin and lincomycin production wastewater. The NARs of AF2 used for abamectin and lincomycin production wastewater treatment were >90% and the SAORs were 2.39 kg NH4+-N·kg MLVSS−1·d−1 and 0.54 kg NH4+-N·kg MLVSS−1·d−1, respectively, which was higher than the traditional biological denitrification process. In summary, AF2 was effective for APW treatment via enhanced ammonia removal efficiency, demonstrating great potential for future industrial wastewater treatment.

Study on treatment of wastewater with low concentration of ammonia-nitrogen by vacuum plate membrane distillation technology.

The removal of low concentration ammonia-nitrogen in industrial wastewater is necessary before discharged into the environment. In this study, vacuum plate membrane distillation (VPMD) technology was utilized and operating parameters such as pH, feed temperature, vacuum degree, feed flow and time were investigated. Based on the experimental data, the heat and mass transfer mechanism and mathematic model were studied. The experimental results show that low solution pH was significantly beneficial to ammonia-nitrogen removal but permeate flux was nearly changeless. At pH = 4, a removal rate up to 93.33% was achieved. Ammonia-nitrogen mainly exists with NH4+ ions in acidic solution, so only water molecules pass through the membrane to acquire the water product in the permeate side. Increasing the temperature of the solution was disadvantageous to the ammonia-nitrogen removal due to membrane pores expanding and the mass transfer coefficient of NH3 molecules increasing; therefore a low temperature was chosen if possible. Because vapor pressure of the feed solution increases exponentially with temperature and results in membrane surface pressure difference increases, therefore increasing the temperature enhances the permeate flux. Raising the vacuum degree enhanced ammonia removal rate and permeate flux obviously, a vacuum degree of 0.09 MPa was chosen for the experiment. The effect of feed flow rate on ammonia-nitrogen removal instead of permeate flux is weak, the reason is that the boundary layer wears thin when the feed flow rate is increased, which is conducive to permeate flux increasing. In a two-parameter model of Knudsen diffusion, Poiseuille flow was chosen to demonstrate the heat and mass transfers in the process of VPMD in the study. Based on the experimental values of permeate flux, two parameters CK and CP in the model were calculated using a nonlinear fitting method software, which indicated that the Knudsen diffusion model more than the Poiseuille flow model was suitable. The maximum values of the relative average deviation (RAD) and root mean square difference (RMSD) of experimental and calculated values with model equations of the permeate flux at the different temperature, vacuum degree and feed flow rate were no more than 8.7% and 3.20 kg · (m2 · h)-1, respectively.

Biological treatment of municipal wastewater using fixed rope media technology: Impact of aeration scheme

This paper characterized a new fixed rope media system to upgrade decentralized and small-scale wastewater treatment plants. A primary effluent of municipal wastewater was treated using two pilot-scale reactors equipped with full-scale sized fixed rope media technology, one of the reactors was aerated using a coarse bubble tube and the other using a custom fine bubble aeration system. The study examined the impact of the aeration scheme and intensities and the COD/NH 3 -N ratio on ammonia and COD removal rates, excessive biofilm growth, slough-off, and microbial communities’ composition. The average biofilm ammonia and COD removal rates ranged from 0.23 ± 0.15 to 0.38 ± 0.26 gNH 3 -N/m 2 .d and 1.35 ± 0.95 to 3.05 ± 1.21 gCOD/m 2 .d, respectively. The fine and coarse bubble reactors showed comparable carbon oxidation rates; however, the fine bubble reactor showed a higher nitrification rate than the coarse bubble reactor at lower aeration intensities despite the similar dissolved oxygen concentration. Correspondingly, an increase in COD/NH 3 -N and excessive biofilm growth decreased the NH 3 -N removal performance but did not affect the COD removal efficiency. Further analysis of the microbial communities composition revealed that the reactors supported a relatively substantial amount of AOB (55 and 63%) and denitrifying bacteria (36 and 21%) with a relatively lower NOB (7 and 8%) and anammox (1 and 8%) species in the fine and coarse bubble aeration reactors, respectively. Overall this study demonstrated the feasibility of one stage fixed rope media to treat COD and ammonia and meet treatment objectives, thus providing an alternative solution to decentralized and smaller plant upgrades. • Ammonia and COD removal efficiency of innovative fixed rope media technology was evaluated. • Different aeration schemes showed minimal impact on the DO concentration but impacted removal performances. • C/N ratio influenced NH 3 -N removal but not COD removal. • Slough off did not impact COD removal; however, it enhanced ammonia removal. • Reactor with the fine bubble aeration supported a relatively higher fraction of denitrifying bacteria.

Metagenomics illuminated the mechanism of enhanced nitrogen removal and vivianite recovery induced by zero-valent iron in partial-denitrification/anammox process

In this study, a novel strategy of zero-valent iron (ZVI) combined with acetic acid was proposed to optimize partial-denitrification/anammox (PD/A) process, and enhanced nitrogen removal mechanism was elucidated through metagenomics. Results showed that the optimal nitrogen and phosphorus removal were as high as 99.50% and 98.37%, respectively, with vivianite being precipitated as the main byproduct. The occurrence of Feammox was a crucial link for enhanced ammonia removal and vivianite recovery. Metagenomic analysis further certified that long-term acclimation of optimization strategy triggered DNRA-based nitrate reducing genes (narY/Z and nrfA) assigned to Candidatus Brocadia, which allow direct uptake of nitrate by the anammox. Additionally, ZVI might act as a new electron donor to decrease organics dependence of PD by reducing the abundance of genes for electron production involved in carbon metabolism. However, FA addition enhanced the relative abundances of genes involved in anammox including nitrogen reduction and oxidation, thereby accelerating nitrogen removal.

Ammonia recovery from simulated anaerobic digestate using a two-stage direct contact membrane distillation process.

Ammonia is a key inorganic contaminant in wastewater and an important nutrient element for agriculture. Herein, a two-stage direct contact membrane distillation (DCMD) system was developed and investigated for ammonia recovery from a synthetic anaerobic digestate. In the 1st stage DCMD (DCMD-1), both ammonia and water moved across MD membrane to realize ammonia separation, while in the 2nd stage (DCMD-2), only water migrated and as a result ammonia was concentrated. It was found that increasing the initial feed solution pH could enhance ammonia removal in the DCMD-1 from 16.0±2.0% (no pH adjustment) to 84.2±1.9% (pH 12). A higher feed solution temperature increased both ammonia flux and water flux. The optimal condition was determined as an initial feed pH of 12, a feed temperature of 60°C, and the 0.6M H2 SO4 adsorption solution. With the addition of the DCMD-2, the ammonia concentration was improved from 3gL-1 to 7.8±0.2gL-1 , which was further enhanced to 26.3±3.0gL-1 after five batches of operation. These results have demonstrated the feasibility of a two-stage DCMD system for ammonia recovery from anaerobic digestate and warrant further investigation of several key issues that may advance this technology. PRACTITIONER POINTS: A two-stage membrane distillation system is developed to remove and recover ammonia from anaerobic digester effluents. The system uses ammonia/ammonium equilibrium to separate ammonia in the 1st stage and then concentrate it in the 2nd stage. A high initial pH of the feed solution plays a key role in achieving high ammonia removal. Minimizing the volume of permeate solution can increase the ammonia concentration.

Preclinical evaluation of liposome-supported peritoneal dialysis for the treatment of hyperammonemic crises

Liposome-supported peritoneal dialysis (LSPD) with transmembrane pH-gradient liposomes was previously shown to enhance ammonia removal in cirrhotic rats and holds promise for the treatment of hyperammonemic crises-associated disorders. The main objective of this work was to conduct the preclinical evaluation of LSPD in terms of pharmacokinetics, ammonia uptake, and toxicology to seek regulatory approval for a first-in-human study. The formulation containing citric acid-loaded liposomes was administered intraperitoneally at two different doses once daily for ten days to healthy minipigs. It was also tested in a domestic pig model of hyperammonemia. The pharmacokinetics of citric acid and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine was linear following intraperitoneal administration of medium and high dose. There was no systemic accumulation following daily doses over ten days. The systemic exposure to phospholipids remained low. Furthermore, the liposome-containing peritoneal fluid contained significantly higher ammonia levels than the liposome-free control, demonstrating efficient ammonia sequestration in the peritoneal space. This was indeed confirmed by the ability of LSPD to decrease plasmatic ammonia levels in artificially induced hyperammonemic pigs. LSPD was well tolerated, and no complement activation-related pseudoallergy reactions were observed. The safety profile, the linear pharmacokinetics of citric acid following repeated administrations of LSPD as well as the linear dose-dependent ammonia sequestration in the peritoneal space provide a strong basis for the clinical investigation of LSPD.

Effect of biosurfactant on ammonia removal from anaerobically digested swine wastewater by multi soil layering treatment bioreactors

ABSTRACT A biosurfactant was harvested from anaerobically digested swine wastewater (ADSW) and employed to enhance ammonia removal in a comparative study using two multiple soil layer bioreactors (MSLs). Results showed that toxicity of the biosurfactant to microorganisms was negligible within the experimental concentration range. Optimal dose of the biosurfactant in MSLs to remove ammonia from ADSW was 0.1 CMC (Critical Micelle Concentration) under different hydraulic loading rate (HLR). For instance, when the HLR was adjusted as 80, 120, 160, and 200 L/(m2·d), the average ammonia removal efficiency in MSL without biosurfactant addition was appeared as 85.6%, 89.2%, 85.2% and 84.1%, respectively, after enhanced by 0.1 CMC of the biosurfactant under the same condition, the average ammonia removal efficiency was improved to 90.1%, 92.6%, 90.3%, and 87.4%, respectively. Inlet ammonia concentration obviously affected ammonia removal, the average ammonia removal efficiency increased rapidly to 93.0% and 89.1% in MSLs (with and without biosurfactant) along with the increasing inlet ammonia concentration from 800 mg/L to 1000 mg/L, and subsequently dropped to 78.9% and 79.7% with a further increase in the inlet ammonia concentration to 1400 mg/L. These results showed that the biosurfactant effectively enhanced ammonia removal by using MSL. Thus, the construction of MSL represented an effective means of reducing ammonia pollution caused by swine wastewater, and the use of biosurfactant was assuredly a promising and feasible option for enhancing the biological activity in MSL bioreactor.

Enhancement of wastewater treatment efficiency through modulation of aeration and blue light on wastewater-borne algal-bacterial consortia

Since few studies have investigated the nitrification and assimilation of nitrogens by algal-bacterial consortia, this study aimed to evaluate the effects of supplementary aeration and blue light on nitrogen removal and biomass growth of algal-bacterial consortia in real domestic wastewater. When blue light was weakly irradiated (500 μmol m−2 s−1), it was found that supplementary aeration enhanced ammonia removal from 38.5% to 96.3% and algal growth from 72.5 mg algae L−1 to 345.3 mg algae L−1 by providing oxygen for nitrification and inorganic carbon for photosynthesis of microalgae. It was also observed that ammonia was consumed first and then nitrate produced by nitrification was assimilated, indicating that diauxic growth of consortia on nitrogen sources occurred. Thus, it was expected that nitrogen removal could be enhanced by lowering nitrification and denitrification loads. Moreover, intense blue light was found to accumulate nitrite by selective photoinhibition of nitrite oxidizing bacteria (NOB) of which c-type cytochrome is known to be photo-bleachable at 408 nm. From these results, it was concluded that favorable conditions for growth and nitrogen removal by algal-bacterial consortia in real wastewater could be established by controlling aeration and light intensity.

Air stripping process for ammonia recovery from source-separated urine: modeling and optimization

BACKGROUND The air stripping process has been widely used to treat wastewater to prevent undesirable substances from impairing the quality of water sources. This study aimed to investigate the operational and economic aspects of air stripping for ammonia recovery from source separated human urine. RESULTS The typical two-film model fails to explain the influence of pH on ammonia recovery. For that reason, modifications to the two-film model were applied to involve ammonia dissociation during mass transfer. It was found that increasing pH enhanced ammonia removal efficiency by promoting the free ammonia fraction in the solution. In addition, high air flow rate and temperature accelerated the stripping process due to the increase in mass transfer coefficient. From the economic point of view, unit operating cost was determined for 80% ammonia recovery. Results indicated that increasing air flow rate and temperature could reduce unit operating cost, whereas high pH could induce high unit operating cost due to the increase in chemical input. CONCLUSION The modified two-film model can precisely estimate the critical values for an economic, efficient stripping process. However, a test-bedding study is required to validate the experimental findings. © 2014 Society of Chemical Industry

Enhanced ammonia removal at room temperature by pH controlled partial nitrification and subsequent anaerobic ammonium oxidation

The Anammox-based processes are suitable for the treatment of wastewaters characterized by a low carbon to nitrogen (C/N) ratio. The application of the Anammox process requires the availability of an effluent with a NO 2−‒ N/NH 4+‒ N ratio composition around 1 g g−1, which involves the necessity of a previous step where the partial nitrification is performed. In this step, the inhibition of the nitrite-oxidizing bacteria (NOB) is crucial. In the present work, a combined partial nitrification-ANaerobic AMmonia OXidation (Anammox) two-units system operated at room temperature (20°C) has been tested for the nitrogen removal of pre-treated pig slurry. To achieve the successful partial nitrification and inhibit the NOB activity, different ammonium/inorganic carbon (NH 4+/IC ) ratios were assayed from 1.19 to 0.82 g NH 4+-N g−1 HCO3‒ C. This procedure provoked a decrease of the pH value to 6.0 to regulate the inhibitory effect over ammonia-oxidizing bacteria caused by free ammonia. Simultaneously, the NOB experienced the inhibitory effect of free nitrous acid which avoided the presence of nitrate in the effluent. The NH 4+/IC ratio which allowed the obtaining of the desired effluent composition (50% of both ammonium and nitrite) was 0.82±0.02 g NH 4+‒ N g−1 HCO 3−‒ C. The Anammox reactor was fed with the effluent of the partial nitrification unit containing a NO 2−‒ N/NH 4+‒ N ratio of 1 g g−1 where a nitrogen loading rate of 0.1 g N L−1 d−1 was efficiently removed.

High Rates of Ammonia Removal in Experimental Oxygen-Activated Nitrification Wetland Mesocosms

While constructed treatment wetlands are very efficient at polishing nitrate from secondary effluent, they are much less effective at removing ammonia. A key factor that limits ammonia oxidation via biological nitrification in vegetated wetlands is low levels of dissolved oxygen. This study evaluated the effectiveness of side-stream oxygenation to enhance ammonia removal in replicate surface-flow experimental mesocosms containing wetland sediment and plants (Typha spp.). Mesocosms had a water volume of 29.5 L, a hydraulic retention time of 5 days, and a hydraulic loading rate of 4.3 cm/d, and were loaded with synthetic secondary effluent contain 10 mg-N/L of ammonia. Relative to nonoxygenated controls, oxygenation increased ammonia removal rates by an order of magnitude. Areal removal rates increased from 40 mg-N/ m2 /d to 450 mg-N/ m2 /d , concentration removal efficiency increased from 10 to 95%, and area-based first-order removal rates increased from <2 m/year to 50–75 m/year. Ammonia removal rates in ...

Application of vacuum membrane distillation for ammonia removal

This study aims to investigate the applicability of membrane distillation for ammonia removal from its aqueous solutions. Among the different recognized membrane distillation configurations, vacuum membrane distillation is applied in the present work for ammonia removal. The effects of different operating parameters on ammonia removal from aqueous solutions of different concentrations have been investigated. Experimental results showed that high feed temperatures, low downstream pressures and high initial feed concentrations and pH levels enhance ammonia removal efficiency. The pH is found to be the most dominant factor. Temperature and concentration polarizations within feed boundary layer proved to have a significant influence on mass transport. High feed flow velocity is an important tool diminishing temperature and concentration polarizations effects. The resistance to mass transfer is found to switch from being predominantly located in the feed side at low feed temperatures and flow velocities to be nearly located within the membrane pores at 55.7 °C and reasonably higher feed flow velocity of 0.84 m/s. Although high feed temperatures and low downstream pressures increase remarkably the total transmembrane flux and the ammonia removal rate, the corresponding ammonia separation factors were decreased. Ammonia removal efficiencies higher than 90% with separation factors of more than 8 were achieved in this study.

Anaerobic digestion of dairy manure with enhanced ammonia removal

Poor ammonia-nitrogen removal in methanogenic anaerobic reactors digesting animal manure has been reported as an important disadvantage of anaerobic digestion (AD) in several studies. Development of anaerobic processes that are capable of producing reduced ammonia-nitrogen levels in their effluent is one of the areas where further research must be pursued if AD technology is to be made more effective and economically advantageous. One approach to removing ammonia from anaerobically digested effluents is the forced precipitation of magnesium ammonium phosphate hexahydrate (MgNH 4PO 4·6H 2O), commonly called struvite. Struvite is a valuable plant nutrient source for nitrogen and phosphorus since it releases them slowly and has non-burning features because of its low solubility in water. This study investigated coupling AD and controlled struvite precipitation in the same reactor to minimize the nitrogen removal costs and possibly increase the performance of the AD by reducing the ammonia concentration which has an adverse effect on anaerobic bacteria. The results indicated that up to 19% extra COD and almost 11% extra NH 3 removals were achieved relative to a control by adding 1750 mg/L of MgCl 2·6H 2O to the anaerobic reactor.

Hepatocellular transplantation for metabolic support in experimental acute ischemic liver failure in rats.

The function of transplanted hepatocytes in acute ischemic liver failure was studied in an experimental model using rats. Ischemic liver failure was induced by occlusion of the proximal portal vein and hepatic artery immediately following extracorporeal portofemoral venous bypass. All rats were bred in a closed colony. Rats in Group 1 were untreated and served as controls (n = 10). Rats in Group 2 received an intrasplenic transplant of hepatocytes (1 x 10(7) cells) 48 h before liver ischemia (n = 10). Serum ammonia and blood glucose were measured before, and 1 h after, ischemia. Serum ammonia was significantly higher than normal (Group 1, 930 micrograms/dL vs < 110 micrograms/dL) after liver ischemia. On the other hand, serum ammonia in group 2 also was elevated (355 micrograms/dL), but significantly less so than in Group 1 (p < 0.001). Blood glucose was lower in both groups after liver ischemia, compared to normal (50-100 mg/dL), but it was higher in Group 2 (30 mg/dL) than in Group 1 (14 mg/dL, p < 0.01). Liver histology 1 h after ischemia showed similar degrees of necrosis in the two groups. Transplanted hepatocytes were viable, and clearly identified in the splenic parenchyma after ischemia. Intrasplenic transplanted hepatocytes provide temporary metabolic support of acute ischemic liver failure in rats, as reflected by enhanced ammonia removal and gluconeogenesis.

Microorganisms and Higher Plants for Waste Water Treatment

AbstractBatch experiments were conducted to compare the waste water treatment efficiencies of plant‐free microbial filters with filters supporting the growth of reeds (Phragmites communis), cattail (Typha latifolia), rush (Juncus effusus), and bamboo (Bambusa multiplex). The experimental systems consisted of two components in series. The first component was an anaerobic settling‐digestion container. The second was a “nonaerated” trough filled with rocks, decreasing from large rocks (up to 7.5‐cm diam) at the bottom, to pea gravel (0.25‐ to 1.3‐cm diam) at the top. The plant‐free microbial filter was equally effective in carbonaceous BOD5 (5‐d biochemical O2 demand) removal. The vascular aquatic plant series enhanced ammonia removal, and consequently improved nitrogenous BOD5 removal. Under the conditions of these experiments, raw sewage with initial BOD5's of 100 mg/L can be upgraded to meet secondary standards with 6 h in component 1, and 6 h in a plant‐free filter or filter using cattail, rush, or reed. When initial BOD5's are approximately 450 mg/L, 24 h in component 1, 29 h in a reed filter are required to meet secondary standards. Total N removal studies were conducted, which demonstrated that a reed system is capable of removing NO3‐N and NH3‐N simultaneously, probably through a common NO2‐N intermediary, then to N2. Overall, the reed system was superior to all others evaluated in this research project.