Stabilization lagoons are economic systems that are built for treatment of municipal, industrial and agricultural wastewater; these systems are used in rural communities. Objective of this article is to present the hydrodynamics flow in lagoon system considering 6 screens with 7 channels containing curved forms with slopes suitable to stabilize the flow along each channel, and approach a piston flow. Hydrodynamics of this system with IBER software was analyzed, where was considered the velocity and hydraulic gradient, using Froude number. Also transport of total suspended solids was modelled. Efficiency in the treatment with this design was evaluated, using parameters such as, pH, conductivity, alkalinity, hardness, total solids, dissolved oxygen, redox potential and Chemical Oxygen Demand (COD). Through the results , a homogeneous transport was observed, mainly dissolved oxygen which was concordant with redox potential and COD, also through the curves, short circuits were minimized , avoiding dead zones and making treatment more efficient , finally were possible to comply with regulations of Mexico NOM-001-SEMARNAT-1996 of discharges and the NOM-003-SEMARNAT-1997 for water of agricultural use.
Natural treatment systems, such as stabilization lagoon systems and wetlands either natural or artificial, represent a very useful alternative to being environmen- tally friendly systems, as well as being an economic option due to low operating and maintenance costs [
A particular case of stabilization lagoons is maturation lagoons; main functions are: 1) nitrification of ammoniac nitrogen, 2) nutrient removal and 3) clarification of effluent [
To avoid short circuits and dead zones, curved shapes with slope were designed in every channel change, which also generated more homogeneous flow. In order to achieve this, a study of hydrodynamic was carried out with IBER Software considering two periods of sampling: winter and spring, taking into account hydraulic flow velocities in each channel, and Froude number for ratio of inertia forces and gravity forces acting on water flow. In order to analyze the behavior in curves shapes with slope, a monitoring parameter of total solids in each channel was used. So as to determine efficiency of screens and curves in lagoon system: temperature, pH, conductivity, dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total solids suspended (TSS), hardness and alkalinity were monitored.
In order to complete municipal wastewater treatment of a horizontal flow sub- surface wetland for rural areas [
mg/L of TSS, 1176.96 ± 53.85 mg/L of BOD and 1923.13 ± 81.66 mg/L of COD in spring.
Hydraulic previous consisting of an anaerobic pre-treatment system,
Lagoon system is built with porous block, as it aims to build such facilities in rural areas for economic reasons and on the other hand it is to take advantage of porosity of the material for fixing bacterial film.
Sampling in each sites selected was monitored for 2 periods: winter and spring 2016, at the same time from 10:00 a.m. to 4:00 p.m. with the purpose of ensure microbial activity. Sampling was carried out at a regular depth of 25 cm with kind bailer samplers at 13:00 hours.
In order to determine the behavior of lagoon system as a function of parameters: temperature, pH, conductivity, redox potential (ORP), dissolved oxygen (DO), total solids suspended (TSS) sites in seven mentioned channels were defined. pH was determined according to the NMX-AA-008-SCFI-2000 [
Alkalinity [
It was important to consider optimization and homogenization of water flow in the input of lagoon system, for which landfills were designed, using Thomson Equation (1) for triangular landfills [
where:
Q = Flow (m3/s).
H = Water from the landfill (m).
Flow rate that enters in lagoon system from wetland was Q = 2 L/s, and for design of landfill was considered from Thomson
For hydrodynamic study in lagoon system, IBER software was used [
where:
h = depth;
Ux, Uy = Horizontal velocities averaged in depth;
G = Acceleration of gravity;
Zs = Free surface elevation;
τs = Friction in free surface due to the friction produced by wind;
ρ = Density of water;
Ω = Angular velocity of rotation of the earth;
Λ = Latitude of the point considered;
Ms, Mx, My = Source/sink sum of mass and moment, through which the modelling is performed.
The variation of parameters: temperature, pH, conductivity, hardness and alkalinity during two sampling periods are presented in
Site | Temperature ˚C | pH | Conductivity mS/cm | Hardness Eq. CaCO3 | Alkalinity Eq. CaCO3 | |||||
---|---|---|---|---|---|---|---|---|---|---|
Winter | Spring | Winter | Spring | Winter | Spring | Winter | Spring | Winter | Spring | |
0 | 17.80 ± 0.73 | 19.80 ± 0.76 | 7.89 ± 0.20 | 7.87 ± 0.31 | 319.60 ± 11.92 | 317.90 ± 8.17 | 136.22 ± 5.15 | 141.12 ± 3.88 | 287.00 ± 7.03 | 277 ± 8.93 |
1 | 18.20 ± 0.695 | 20.10 ± 0.62 | 7.87 ± 0.30 | 7.83 ± 0.30 | 319.10 ± 13.11 | 316.83 ± 7.86 | 132.43 ± 6.03 | 138.43 ± 4.78 | 281.00 ± 8.33 | 272 ± 10.91 |
2 | 18.40 ± 0.79 | 20.40 ± 0.64 | 7.83 ± 0.22 | 7.82 ± 0.31 | 318.90 ± 10.24 | 315.20 ± 10.46 | 130.40 ± 4.06 | 130.40 ± 3.90 | 279.00 ± 7.45 | 270 ± 8.48 |
3 | 18.80 ± 0.70 | 20.60 ± 0.88 | 7.86 ± 0.21 | 7.80 ± 0.28 | 319.40 ± 15.11 | 316.86 ± 9.47 | 132.03 ± 4.33 | 138.03 ± 3.96 | 282.00 ± 8.49 | 273 ± 8.93 |
4 | 19.40 ± 0.74 | 20.90 ± 0.85 | 7.84 ± 0.31 | 7.72 ± 0.27 | 317.12 ± 9.16 | 314.20 ± 12.60 | 126.60 ± 4.34 | 125.60 ± 4.05 | 278.00 ± 7.42 | 271 ± 8.63 |
5 | 19.60 ± 0.83 | 21.30 ± 0.66 | 7.85 ± 0.24 | 7.74 ± 0.31 | 315.50 ± 8.77 | 314.00 ± 8.71 | 123.55 ± 4.07 | 121.55 ± 3.59 | 280.00 ± 7.90 | 268 ± 10.72 |
6 | 19.90 ± 0.83 | 21.80 ± 0.66 | 7.85 ± 0.26 | 7.69 ± 0.26 | 317.22 ± 9.67 | 315.87 ± 9.19 | 126.38 ± 5.18 | 126.38 ± 5.05 | 277.00 ± 8.54 | 271 ± 9.35 |
7 | 20.20 ± 0.80 | 22.00 ± 0.94 | 7.82 ± 0.30 | 7.66 ± 0.32 | 316.90 ± 12.99 | 315.25 ± 9.55 | 119.85 ± 3.32 | 121.85 ± 4.43 | 268.00 ± 7.38 | 268 ± 9.78 |
8 | 20.50 ± 0.90 | 22.60 ± 0.73 | 7.78 ± 0.31 | 7.68 ± 0.30 | 317.56 ± 10.22 | 315.00 ± 9.92 | 115.45 ± 4.75 | 117.25 ± 3.12 | 266.00 ± 8.28 | 263 ± 10.58 |
9 | 21.30 ± 0.80 | 22.90 ± 1.11 | 7.76 ± 0.26 | 7.63 ± 0.28 | 317.81 ± 12.24 | 315.37 ± 12.84 | 117.35 ± 4.55 | 120.35 ± 4.87 | 268.00 ± 7.42 | 265 ± 9.86 |
10 | 21.70 ± 0.88 | 23.20 ± 0.80 | 7.74 ± 0.25 | 7.69 ± 0.24 | 317.43 ± 11.85 | 314.37 ± 9.97 | 102.73 ± 4.23 | 118.73 ± 4.55 | 264.00 ± 8.32 | 262 ± 10.17 |
11 | 22.30 ± 0.83 | 23.60 ± 0.98 | 7.73 ± 0.30 | 7.65 ± 0.30 | 316.56 ± 8.64 | 314.00 ± 8.73 | 102.18 ± 4.17 | 112.18 ± 3.20 | 260.00 ± 7.23 | 256 ± 10.56 |
12 | 22.50 ± 0.83 | 24.70 ± 1.13 | 7.73 ± 0.22 | 7.67 ± 0.24 | 317.18 ± 13.13 | 314.56 ± 7.61 | 104.95 ± 3.29 | 114.95 ± 3.98 | 263.00 ± 8.44 | 259 ± 8.97 |
13 | 22.70 ± 1.06 | 25.60 ± 0.88 | 7.69 ± 0.30 | 7.64 ± 0.27 | 316.64 ± 10.52 | 313.78 ± 9.95 | 103.13 ± 3.04 | 110.13 ± 3.44 | 261.00 ± 6.95 | 255 ± 8.14 |
14 | 22.30 ± 0.98 | 25.20 ± 0.95 | 7.65 ± 0. 35 | 7.62 ± 0.31 | 317.55 ± 11.84 | 313.32 ± 13.38 | 100.30 ± 2.68 | 100.30 ± 4.12 | 257.00 ± 7.37 | 252 ± 10.15 |
15 | 21.70 ± 0.72 | 25.40 ± 1.08 | 7.67 ± 0.30 | 7.66 ± 0.27 | 318.87 ± 9.31 | 313.98 ± 14.03 | 103.53 ± 3.39 | 111.53 ± 3.32 | 260.00 ± 8.47 | 258 ± 11.40 |
16 | 21.50 ± 0.72 | 24.70 ± 0.97 | 7.63 ± 0.33 | 7.68 ± 0.30 | 317.59 ± 10.32 | 312.86 ± 10.97 | 101.70 ± 4.07 | 109.70 ± 4.58 | 256.00 ± 7.91 | 253 ± 9.41 |
17 | 20.60 ± 0.88 | 23.80 ± 0.82 | 7.66 ± 0.22 | 7.65 ± 0.25 | 314.87 ± 12.69 | 312.27 ± 10.71 | 99.80 ± 3.54 | 100.80 ± 4.12 | 250.00 ± 7.13 | 251 ± 9.75 |
18 | 20.30 ± 0.75 | 23.20 ± 1.06 | 7.66 ± 0.29 | 7.67 ± 0.30 | 317.53 ± 11.18 | 312.87 ± 9.94 | 101.60 ± 4.23 | 108.60 ± 4.11 | 252.00 ± 7.82 | 253 ± 10.42 |
19 | 19.60 ± 0.69 | 22.20 ± 0.90 | 7.62 ± 0.33 | 7.69 ± 0.30 | 316.38 ± 9.08 | 312.30 ± 9.09 | 100.80 ± 3.84 | 102.80 ± 3.27 | 247.00 ± 7.51 | 250 ± 8.87 |
20 | 19.20 ± 0.62 | 22.70 ± 0.88 | 7.63 ± 0.34 | 7.71 ± 0.37 | 314.82 ± 9.70 | 312.00 ± 11.13 | 90.68 ± 2.80 | 99.97 ± 40.29 | 241.00 ± 6.63 | 245 ± 9.46 |
21 | 18.30 ± 0.74 | 20.30 ± 0.64 | 7.58 ± 0.20 | 7.65 ± 0.24 | 311.77 ± 7.98 | 310.72 ± 11.66 | 90.28 ± 2.62 | 97.28 ± 3.12 | 238.00 ± 5.55 | 242 ± 7.72 |
resulted with values of 75 - 150, reason why it is considered Moderately Hard (MD) according criteria of international hardness [
In
Overall, a tendency to decrease in concentration of TSS was observed, being scarce on departure at exit of lagoon system, which indicates a homogeneous sedimentation process along each channel.
Dissolved Oxygen (DO) variation in lagoon system is observed in
important to mention that water which entering in system, comes from a treatment sub-surface wetland of horizontal flow [
Finally, the concentration improves at the exit of each curve and during straight sections. DO behavior is consistent with the redox potential (ORP) (
In
It is also observed that at site 1 (entrance to the system) is the site with the most negative value in both stations, as the flow advances along the channels, an improvement in conductivity is observed, behavior that coincides with the Improvement of DO and COD. It can also be observed that at the beginning of each ORP curve it acquired negative values.
slope, BOD increased, due to the fact that there was more accumulation of biodegradable material, the degradation was increasing until its decrease in the out- put of lagoon system.
COD is a representative measure of organic contamination in an effluent, parameter which will be controlled within the different discharge regulations.
In
Froude number was determinate, which relates forces of inertia and gravity, implicitly considering velocity and hydraulic gradient at each point of path the water flow, evaluating type of regime.
that increase at the end of each of curves, which is due to hydraulic jump caused by slope change in curves. A change in critical regime was presented, for example, in changes in slope. The flow in critical regime (or in its environs) was unstable [
This software was also used to model TSS transport in the lagoon system (
% BOD | Winter | Spring | % COD | Winter | Spring |
---|---|---|---|---|---|
First channel | 12.34 | 12.20 | First channel | 13.53 | 8.05 |
Second channel | 2.31 | 9.15 | Second channel | 2.60 | 9.52 |
Third channel | 4.42 | 8.96 | Third channel | 5.48 | 1.56 |
Fourth channel | 2.92 | 1.67 | Fourth channel | 6.02 | 5.77 |
Fifth channel | 9.50 | 8.51 | Fifth channel | 5.40 | 8.32 |
Sixth channel | 7.42 | 6.81 | Sixth channel | 28.33 | 7.18 |
Seventh channel | 26.17 | 32.99 | Seventh channel | 30.95 | 38.49 |
Input-output | 74.11 | 71.69 | Input-output | 64.90 | 67.99 |
up in each channel. Regarding BOD in the first and seventh channels, the best efficiency was observed in the sixth and seventh channels for COD.
Finally in
In case of lagoon system, the treatment for TSS was better in winter, because fewer solids were introduced in wetland. The BOD was slightly better in winter, where the flow velocity can be influenced by the curved forms of each channel that avoid short circuits and therefore dead zones, same can be said of COD.
Design of 7 screens in lagoon helped to approximate the total water flow to a piston flow, which was optimized by the slopes in curves that induced to cross to the flow in sections where tangential forces were distributed evenly, avoiding thus presence of dead zones, short circuits and dispersed flows.
In addition, a good distribution of the hydraulic flow was achieved, which was demonstrated through behavior of DO, OPR, TSS, BOD and COD, as shown in graphs. With IBER software, it was possible to obtain velocity distribution and
Pre-treatment system | |||||||
---|---|---|---|---|---|---|---|
Winter | Spring | ||||||
Parameter (mg/L) | Input | Output | % Efficiency | Input | Output | % Efficiency | |
TSS | 5.667 | 1.728 | 69.51 | 4.176 | 1.528 | 63.41 | |
BOD | 654.86 | 398.77 | 39.11 | 1176.96 | 701.26 | 40.42 | |
COD | 1064.48 | 568.13 | 46.63 | 1923.13 | 986.67 | 48.69 | |
Treatment by wetland | |||||||
Winter | Spring | ||||||
Parameter (mg/L) | Input | Output | % Efficiency | Input | Output | % Efficiency | |
TSS | 1.728 | 0.842 | 51.30 | 1.528 | 0.890 | 41.75 | |
BOD | 398.77 | 68.921 | 82.72 | 701.26 | 93.581 | 86.66 | |
COD | 568.13 | 111.50 | 80.37 | 986.66 | 150.03 | 84.79 | |
Treatment by lagoon system | |||||||
Winter | Spring | ||||||
Parameter (mg/L) | Input | Output | % Efficiency | Input | Output | % Efficiency | |
TSS | 0.842 | 0.051 | 93.94 | 0.890 | 0.014 | 51.30 | |
BOD | 68.92 | 17.85 | 74.11 | 93.58 | 26.49 | 71.69 | |
COD | 111.50 | 39.14 | 64.90 | 150.45 | 48.17 | 67.99 | |
Total system treatment | |||||||
Winter | Spring | ||||||
Parameter (mg/L) | % Efficiency | % Efficiency | |||||
TSS | 99.10 | 99.19 | |||||
BOD | 97.27 | 97.75 | |||||
COD | 96.32 | 91.52 | |||||
Froude number in different sections, also modelling the transport of TSS, which allowed knowing areas susceptible to TSS saturation. The slope change in curve reduces the bottom drag of sediments, producing a slight decrease in flow velocity, causing the total solids to be retained in pre-curve sections.
When analyzing removal rates of both the lagoon and entire treatment system, it was observed that lagoon system allowed completing the treatment in compliance with Mexican norm NOM-001-SEMARNAT-1996 of discharges and NOM-003- SEMARNAT-1997 for agricultural water.
García-Martínez, M., Osornio-Berthet, L.J., Solís-Correa, H.E., López-Chuken, U.J., Beltrán-Rocha, J.C. and Barceló-Quintal, I.D. (2017) Determination of Hydrodynamics in Municipal Waste Water by a Lagoon System with Screens. Journal of Environmental Protection, 8, 330-343. https://doi.org/10.4236/jep.2017.83025