Comparison of operational design criteria for subsurface flow constructed wetlands for wastewater treatment

2001 ◽  
Vol 43 (11) ◽  
pp. 301-308 ◽  
Author(s):  
K. M. Leonard ◽  
G. W. Swanson
Keyword(s):  
Wastewater Treatment ◽  
Constructed Wetlands ◽  
Rate Constant ◽  
Environmental Protection Agency ◽  
Reaction Rate ◽  
Subsurface Flow ◽  
Plug Flow ◽  
Reaction Rate Constant ◽  
Design Standards ◽  
Design Models

Many communities are investigating the use of constructed wetlands as a simple, viable alternative to poorly operating on-site wastewater treatment. Currently, the most popular design models in the U.S.A. for subsurface flow units are the US Environmental Protection Agency (EPA) and the Tennessee Valley Authority (TVA) methods. However, there has been limited data verifying if the operating performance is up to design standards. In order to address this problem, this paper documents the performance of such treatment systems over a broad range of conditions in North Alabama. The operational data is used to determine a best-fit value of reaction rate constant and proposes improved input parameters for both design models. According to this data, the average plug-flow reaction rate constant was calculated to be 0.70 d-1 for the EPA method, while the recommended organic loading criterion is 11.4 m2/kg BOD5 per day into the wetland for the TVA method.

Kinetics of organic matter and ammonia removal in horizontal reed beds treating wastewater in Nepal

2015 ◽  
Vol 72 (11) ◽  
pp. 1981-1987
Author(s):  
Keshav Raj Bista ◽  
Nawa Raj Khatiwada ◽  
Srijana Khyaju
Keyword(s):  
Organic Matter ◽  
Wastewater Treatment ◽  
Rate Constant ◽  
Rational Design ◽  
Reaction Rate ◽  
Subsurface Flow ◽  
Reaction Rate Constant ◽  
Climatic Conditions ◽  
Ammonia Removal ◽  
Design Criteria

In Nepal, both horizontal bed and vertical bed subsurface flow constructed wetlands have been used for wastewater treatment. However, these units were designed based on the empirical findings from other countries. The rational design criteria developed so far has some limitations as the performance of the units is sensitive to the behaviour of the microorganisms, climatic conditions and other attributes pertaining to the local contexts. Secondly, only limited numbers of studies have been carried out to assess the performance of these systems leading to the development of rationale design criteria. Considering these facts, the major objectives of the study were set to: (1) evaluate the performance of the subsurface flow reed bed system in terms of organic matter and ammonia removal; (2) estimate the reaction rate constant and effective specific surface area; (3) assess the relationship between performance and age of the system; and (4) investigate the dynamic behaviour of the reaction rate constant. The study was carried on three full-scale domestic wastewater treatment units and one pilot-scale ranging the age of horizontal beds from 1 to 5 years.

Reciprocating constructed wetlands for treating industrial, municipal and agricultural wastewater

2001 ◽  
Vol 44 (11-12) ◽  
pp. 399-405 ◽  
Author(s):  
L. Behrends ◽  
L. Houke ◽  
E. Bailey ◽  
P. Jansen ◽  
D. Brown
Keyword(s):  
Wastewater Treatment ◽  
Constructed Wetlands ◽  
Environmental Protection Agency ◽  
Subsurface Flow ◽  
Domestic Wastewater ◽  
High Strength ◽  
Time Frequency ◽  
Operating Technique ◽  
Tennessee Valley ◽  
Subsurface Flow Constructed Wetlands

Scientists at the Tennessee Valley Authority (TVA), and in collaboration with the U.S. Environmental Protection Agency (EPA), are continuing to develop and refine an innovative wastewater treatment system referred to as reciprocating subsurface-flow constructed wetlands. Reciprocation relates to patented improvements in the design and operation of paired subsurface-flow constructed wetlands, such that contiguous cells are filled and drained on a frequent and recurrent basis. This operating technique turns the entire wetland system into a fixed-film biological reactor, in which it is possible to control redox potential in alternating aerobic and anaerobic zones. Reciprocating systems enable manipulation of wastewater treatment functions by controlling such parameters as hydraulic retention time, frequency of reciprocation, reciprocation cycle time, depth of reciprocation, and size and composition of substrate. These improved wetland technologies have been used for treating municipal/domestic wastewater, high strength animal wastewater, and mixed wastewater streams containing acids, recalcitrant compounds, solvents, antifreeze compounds, heavy metals, explosives, and fertilizer nutrients. Results from selected treatability studies and field demonstrations will be summarized with respect to conceptual design and treatment efficacy.

scholarly journals Determination of exothermic batch reactor specific model parameters

2019 ◽  
Vol 292 ◽  
pp. 01063
Author(s):  
Lubomír Macků
Keyword(s):  
Rate Constant ◽  
Reaction Rate ◽  
Batch Reactor ◽  
Specific Model ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
First Order Reaction ◽  
Model Parameters ◽  
Reactor Model ◽  
First Order

An alternative method of determining exothermic reactor model parameters which include first order reaction rate constant is described in this paper. The method is based on known in reactor temperature development and is suitable for processes with changing quality of input substances. This method allows us to evaluate the reaction substances composition change and is also capable of the reaction rate constant (parameters of the Arrhenius equation) determination. Method can be used in exothermic batch or semi- batch reactors running processes based on the first order reaction. An example of such process is given here and the problem is shown on its mathematical model with the help of simulations.

Performance of Photocatalytic Microfiltration with Hollow Fiber Membrane

2007 ◽  
Vol 544-545 ◽  
pp. 95-98 ◽  
Author(s):  
Jong Tae Jung ◽  
Jong Oh Kim ◽  
Won Youl Choi
Keyword(s):  
Heavy Metals ◽  
Humic Acid ◽  
Rate Constant ◽  
Hollow Fiber ◽  
Reaction Rate ◽  
Hollow Fiber Membrane ◽  
Membrane Surface ◽  
Reaction Rate Constant ◽  
Operational Parameters ◽  
Tio2 Particles

The purpose of this study is to investigate the effect of the operational parameters of the UV intensity and TiO2 dosage for the removal of humic acid and heavy metals. It also evaluated the applicability of hollow fiber microfiltration for the separation of TiO2 particles in photocatalytic microfiltration systems. TiO2 powder P-25 Degussa and hollow fiber microfiltration with a 0.4 μm nominal pore size were used for experiments. Under the conditions of pH 7 and a TiO2 dosage 0.3 g/L, the reaction rate constant (k) for humic acid and heavy metals increased with an increase of the UV intensity in each process. For the UV/TiO2/MF process, the reaction rate constant (k) for humic acid and Cu, with the exception of Cr in a low range of UV intensity, was higher compared to that of UV/TiO2 due to the adsorption of the membrane surface. The reaction rate constant (k) increased as the TiO2 dosage increased in the range of 0.1~0.3 g/L. However it decreased for a concentration over 0.3 g/L of TiO2. For the UV/TiO2/MF process, TiO2 particles could be effectively separated from treated water via membrane rejection. The average removal efficiency for humic acid and heavy metals during the operational time was over 90 %. Therefore, photocatalysis with a membrane is believed to be a viable process for humic acid and heavy metals removal.

Reaction rate constant of SO3+ NH3in the gas phase

1990 ◽  
Vol 95 (D9) ◽  
pp. 13981 ◽  
Author(s):  
Gaunlin Shen ◽  
Masako Suto ◽  
L. C. Lee
Keyword(s):  
Gas Phase ◽  
Rate Constant ◽  
Reaction Rate ◽  
Reaction Rate Constant

Prediction of Chemical Reaction Yield in a Microreactor and Development of a Pilot Plant Using the Numbering-Up of Microreactors

2010 ◽  
Author(s):  
Shigenori Togashi ◽  
Yukako Asano ◽  
Yoshishige Endo
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Chemical Reaction ◽  
Rate Constant ◽  
Pilot Plant ◽  
Reaction Rate ◽  
Main Product ◽  
Reaction Rate Constant ◽  
Reaction Yield ◽  
Production Scale

The chemical reaction yield was predicted by using Monte Carlo simulation. The targeted chemical reaction of a performance evaluation using the microreactor is the consecutive reaction. The main product P1 is formed in the first stage with the reaction rate constant k1. Moreover, the byproduct P2 is formed in the second stage with the reaction rate constant k2. It was found that the yield of main product P1 was improved by using a microreactor when the ratio of the reaction rate constants became k1/k2 >1. To evaluate the Monte Carlo simulation result, the yields of the main products obtained in three consecutive reactions. It was found that the yield of the main product in cased of k1/k2 >1 increased when the microreactor was uesd. Next, a pilot plant involving the numbering-up of 20 microreactors was developed. The 20 microreactor units were stacked in four sets, each containing five microreactor units arranged. The maximum flow rate when 20 microreactors were used was 1 × 104 mm3/s, which corresponds to 72 t/year. Evaluation of the chemical performance of the pilot plant was conducted using a nitration reaction. The pilot plant was found to capable of increasing the production scale without decreasing the yield of the products.

scholarly journals Kinetics and Thermodynamics Study of Ultrasound-Assisted Depolymerization of k-Carrageenan in Acidic Solution

2020 ◽  
Vol 15 (1) ◽  
pp. 280-289
Author(s):  
Ratnawati Ratnawati ◽  
Nita Indriyani
Keyword(s):  
Molecular Weight ◽  
Rate Constant ◽  
Reaction Rate ◽  
Acidic Solution ◽  
Biomedical Application ◽  
Bond Cleavage ◽  
Reaction Rate Constant ◽  
Order Kinetic ◽  
Kinetics And Thermodynamics ◽  
Ultrasound Assisted

K-carrageenan is a natural polymer with high molecular weight ranging from 100 to 1000 kDa. The oligocarrageenan with low molecular weight is widely used in biomedical application. The aim of this work was to depolymerize k-carrageenan in an acidic solution with the assistance of ultrasound irradiation. The ultrasonication was conducted at various pH (3 and 6), temperatures (30-60 °C), and depolymerization time (0-24 minutes). The results show that the depolymerization reaction follows pseudo-first-order kinetic model with reaction rate constant of 1.856×10-7 to 2.138×10-6 s-1. The reaction rate constant increases at higher temperature and lower pH. The Q10-temperature coefficients of the depolymerization are 1.25 and 1.51 for pH 6 and 3, respectively. The enthalpy of activation (ΔH‡) and the Gibbs energy of activation (ΔG‡) are positive, while the entropy of activation (ΔS‡) is negative, indicating that the activation step of the ultrasound-assisted depolymerization of k-carrageenan is endothermic, non-spontaneous, and the molecules at the transition state is more ordered than at the ground state. The ΔH‡ and the ΔS‡ are not affected by temperature, while the ΔG‡ is a weak function of temperature. The ΔH‡ and ΔS‡ become smaller at higher pH, while the ΔG‡ increases with the increase of pH. The kinetics and thermodynamics analysis show that the ultrasound-assisted depolymerization of k-carrageenan in acidic solution is possibly through three mechanisms, i.e. bond cleavage due to cavitational effect of microbubbles, hydroxyl radical and hydrogen peroxide, as well as proton. Copyright © 2020 BCREC Group. All rights reserved 

Sign in / Sign up

Export Citation Format

Share Document