OUR Tests Research Articles

Stability of partial nitritation in a sequencing batch reactor fed with high ammonium strength old urban landfill leachate

The aim of this study is to investigate the stability of partial nitritation in a lab-scale sequencing batch reactor (PN-SBR) fed with high ammonium strength old municipal landfill leachate without pH adjustment, bicarbonate addition and low dissolved oxygen control. Long sludge retention of over 120 days was applied for the PN-SBR. The PN-SBR, which run over 250 days used the old urban landfill leachate containing 3096 mg NH₄⁺-N l⁻1, 12960 mg HCO₃ l⁻1, and influent HCO₃⁻:NH₄⁺ molar ratio of 1.06. After 75 days of operation, the partial nitritation achieved stability when the effluent nitrite to ammonium molar ratio obtained in the range of 1.0–1.32, which were suitable for feeding to an anammox reactor. The effluent NO₃⁻-N concentration was always below 20 mg N l⁻1. The maximum FA concentration reached 506 mg NH3-N l−1 at hour 26th during the cycle of 73 h. Even though old land fill leachate mainly contained refractory COD, COD removal efficiency achieved about 11%. The OUR tests show that the maximum growth rate μmax, Ko, Ks and yield coefficient YX/N of AOB were 0.12 day−1, 1.35 mg O2 l−1, 53 mg NH4+-N l−1 and 0.26 mgVSS mg−1 NH4+-N, respectively.

Application of combined physicochemical and biological processes for enhanced treatment of avermectin fermentation wastewater

This paper aimed at developing the enhanced biological treatment processes for treating avermectin fermentation wastewater (AFW). After UASB treatment and chemical coagulation, the pretreated AFW was subsequently flowed into a rCAA reactor (reactor with repeated coupling of aerobes and anaerobes using macroporous carriers) system for further pollutant degradation and excess sludge reduction. By the treatment with chemical coagulation, COD, total nitrogen and total phosphorus concentration of treated AFW were eliminated to 550-700 mg/L, 130-160 mg/L and 1 mg/L, respectively, and the dark color of the wastewater was greatly bleached. After this decolorized wastewater was treated by the following rCAA bioreactor, the COD could be reduced to around 200-300 mg/L, while the further decrease of COD less than 200 mg/L was difficult. The Biolog analysis and OUR test for the water treated by rCAA bioreactor demonstrated that the effluent from chemical coagulation contained some unknown compounds with low biodegradability and would simplify the microbial community in the subsequent rCAA reactor.

Side effects of flux enhancing chemicals in membrane bioreactors (MBRs): study on their biological toxicity and their residual fouling propensity

Soluble and colloidal materials like soluble microbial products (SMP) or extracellular polymeric substances (EPS) are considered to be major foulants in membrane bioreactors (MBRs). Removing these fouling causing substances is thus thought to reduce the fouling of the membrane in general. In addition to traditional strategies for fouling prevention which mostly try to remedy the effects of fouling by air scour, etc., the new and promising method of adding chemicals is being investigated here. Previous tests with 30 different substances have shown that several of these reduce SMP concentration in the supernatant and enhance filtration. Nevertheless, additive dosing might have unknown side effects in filtration systems. Results presented in this study indicate that these additives may themselves cause severe fouling on different membranes if they remain unbound in the liquid phase. Therefore, the thorough control of the dosing rate of these chemicals will be of paramount importance in full scale applications. Biological toxicity of additives was measured in terms of respiration. OUR tests did not show inhibiting effects for most additives. Chitosan even showed an enhanced OUR due to biodegradability. Oxygen transfer could be enhanced for 25% with the addition of a polymer.

Catalytic Wet-oxidation of a Mixed Liquid Waste: COD and AOX Abatement

A series of catalytic wet oxidation (CWO) reactions, at temperatures of 430-500 K and in a batch bench-top pressure vessel were carried out utilizing a strong wastewater composed of landfill leachate and heavily organic halogen polluted industrial wastewater. A CeO2-SiO2 mixed oxide catalyst with large surface area to assure optimal oxidation performance was prepared. The catalytic process was examined during batch reactions controlling Chemical Oxygen Demand (COD) and Adsorbable Organic Halogen (AOX) parameters, resulting AOX abatement to achieve better effect. Color and pH were also controlled during batch tests. A simple first order-two stage reaction behavior was supposed and verified with the considered parameters. Finally an OUR test was carried out to evaluate biodegradability changes of wastewater as a result of the catalytic reaction.

A Real Time Toxicity Bioassay for Activated Sludge Reactor

Activated sludge reactor is commonly employed for the secondary treatment of industrial wastewater, showing a high purification yield, operating simplicity and cost-effectiveness. Nevertheless, industrial wastewater generally contain numerous organic and inorganic compounds which are not biodegradable; heavy metals are often found in effluents from electroplating and metal-processing industries, manufacturing of paints, plastics, scientific instruments, salts are found in wastewater from production of pesticides, pharmaceutical and food industry, waste-dump percolating water. Primary treatments are often designed to reduce heavy metal and salt contents in wastewater, nevertheless trace concentrations persist and may reach the biological reactor, resulting in biomass inhibition and dramatic loss in purification efficiency. Respirometry through Oxygen Uptake Rate measurement is one of the most rapid and reliable methods to assess the inhibition of activated sludge. In previous studies toxicity tests for specific compounds have been performed following different procedures and attaining heterogeneous results. In this work a simple modification of the configuration is proposed, in order to assess in real time the toxicity and the inhibiting effect of the incoming wastewater before it reaches the reactor. A sample is drawn from the influent and a respirometric test is performed on mixed liquor collected from the reactor itself. If the inhibition exceeds the limit, the influent is sent to storage and to an alternative treatment. Preliminary experiments were carried out with bench-scale CSTR, supplied with synthetic wastewater. Copper sulphate and sodium chloride were chosen as inhibiting compounds, supplied separately to batch samples of activated sludge in shock load at different concentrations. Copper concentration in the mixed liquor was measured by atomic absorption and salt concentration was determined through conductance measures. Inhibition up to 90% was evaluated by OUR test with short response time, demonstrating the suitability of this tool to a real time toxicity bioassay for activated sludge reactor.

Inhibition of Nitrification by Heavy Metals and Organic Compounds: The ISO 9509 Test

Nitrification is the most sensitive part in the biologic nutrient removal of wastewaters, with the autotrophic nitrifying biomass being approximately 10 times more sensitive than its aerobic heterotrophic counterpart. The growth rate is much lower and strongly dependent on temperature, substrate concentration, oxygen content, pH, and the presence of inhibiting components. Many kinds of inhibitory compounds are present in wastewater. Some organic compounds and also heavy metals fall within this category. The article assesses these inhibitory effects, and experiments were carried out with representative compounds, that is, Zn2+ and Cu2+ as heavy metals and Ethylbenzene, Chlorobenzene, Trichloroethylene, and Phenol as the organic compound inhibitors. Among the different techniques available to assess the toxicity of components upon the activated sludge process in general, and the nitrification step in particular, respirometry has frequently been used to quantify the degree of inhibition and to study the effects on the specific growth rate of the nitrifying biomass. The present experiments use the ISO 9509 test, which is less tedious and time-consuming and based upon the rate of nitrification (against rate of oxygen uptake rate in the OUR test). The inhibition degree is given as a relationship of dose vs. effects for certain concentrations of inhibitors. The results of these ISO experiments are compared with the results of an inhibition study based on the measurement of the growth rate using the OUR test. By way of additional illustration, the ISO test is also carried out to measure toxic effects of industrial wastewater and diluted industrial wastewater. The inhibition results are categorized according to the degree of inhibition as IC50 (concentration producing 50% inhibition), IC20 (20%), and NOEC (no observed effect concentration). The results reveal that, in general, OUR tests yield a too low indication of the toxicity, with higher IC50 values, than tests based upon measuring the rate of nitrification. The discrepancy is probably the result of the short time of contact between the toxic component and the activated sludge in the OUR procedure. Repeat OUR tests over several days, moreover, give largely different results. The tests using the rate of nitrification give a more direct indication of the inhibition effect on nitrifiers.

A simple biological method to estimate the readily biodegradable organic matter in wastewater

A simple method was proposed to measure the readily biodegradable COD in wastewater. The method, denoted as the single-OUR method, is based on monitoring the oxygen concentration decrease in a single oxygen utilization measurement. The oxygen consumption related to readily biodegradable COD can be estimated from the oxygen concentration profile. In order to transfer this oxygen consumption to the readily biodegradable COD a calibration curve is needed. For the evaluation of the method a batch OUR test was performed in parallel. A good agreement between the two methods was obtained.