Lake Restoration Technologies a short review

Transcription

1 JU AN ICÓ ENVI RONM ENT AL CONSUL T AN TS LTD. International consulting firm on high-tech low-cost low-energy solutions for warm climates JU AN ICÓ CONS UL TORES AM BIENTAL ES LTD. Consultora internacional en soluciones avanzadas de bajo costo y energía para climas cálidos Ram On, Israel Phone juanico@juanico.co.il Website: Lake Restoration Technologies a short review ( lake remediation / lake rehabilitation / lake recovery ) Selecting the best cost/benefit technology for lake restoration There are numerous different technologies for the restoration of polluted lakes and reservoirs Each technology solves a different problem and has its advantages and disadvantages The selection of the proper technology depends on the characteristics of the lake: o small / large o deep / shallow o warm / cold o stratified / non stratified o internal loading / external loading o etc. The selection of the best technology for the restoration of a specific lake is a difficult task. Juanicó - Environmental Consultants Ltd. has the full know-how and experience to perform a diagnosis of the situation of a lake and select the best cost/benefit technologies that can be applied to solve the problem. Figure 1 - Restored Hula Lake in Northern Israel, includes an artificial island 1

2 Main available technologies for lake restoration ONE PAGE ABSTRACT 1. Reduce point-source pollution (external loading) o construction / recovery / upgrade of sewage treatment plants o treatment of river water entering the lake 2. Reduce diffuse pollution (external loading) o fertilizer control in agriculture surrounding the lake o urban and road storm water treatment o vegetation strips / bands surrounding the lake o land management in the catchment basin 3. Reduce pollution from lake sediments (internal loading) o mechanical removal of sediments o bioaugmentation for biological degradation of organic matter o trapping P and other pollutants by coagulation o avoid resuspension of sediments by wind 4. Removal of nutrients from lake water o floating constructed wetlands o in-lake nitrification/denitrification o harvesting of weeds and water hyacinth 5. Ecological manipulation / biological control o control of algae and blue-green (cyanobacteria) blooms ultrasound P control o introduction of sanitary fish for plankton, weeds, organic matter in sediments, mosquito, etc. o stratification rupture (de-stratification) and aeration of sediments 6. Removal of garbage / litter / trash 7. Construction of artificial islands and/or coastal land o for disposal of sediments being removed from the lake o to reduce wind resuspension of sediments at downward coast o to pay for the cost of lake restoration by selling new valuable land areas o to eliminate undesirable coastal swamps that may be a source of mosquitoesmalaria problems 2

3 Reduce point-source pollution (external loading) Construction / recovery / upgrade of sewage treatment plants Sewage is in most cases the main cause of lake pollution. Sewage treatment plants drastically reduce the loading to the lake (or to the river reaching the lake) but in many cases the existing sewage treatment plants do not work properly just due to poor operation & maintenance, or because sewage flow increased over the plant capacity. Figure 2 - Sewage treatment plant and wastewater reservoir in Northern Israel - semi-intensive technology 3

4 Treatment of river water entering the lake In rivers with a limited flow, it is possible to treat almost all the river flow in constructed wetlands. An alternative is to perform out-of-river coagulation and settling for removal of solids and part of phosphorus. Or in-river settling by constructing an artificial settling area in river mouth (a kind of artificial delta in the lake). Figure 3 - River Shchem Israel, out-of-river water treatment by coagulation and settling 4

5 Reduce diffuse pollution (external loading) Diffuse pollution enters the lake/river from sparse sources, mainly by drainage. Fertilizer use in agriculture surrounding the lake Farmers generally use more fertilizers than necessary and fertilizer is sometimes applied in a wrong way. Fertilizer vendors use to recommend high applications above real needs in order to increase their benefits. The result is pollution of rivers and lakes by fertilizers. It is possible to reduce this loading to rivers and lakes by guiding the farmers towards proper application of fertilizers. Figure 4 International course of fertilization and irrigation at CINADCO - Israel Urban - road storm water treatment Urban - road storm water may bring a heavy load of pollutants to rivers and lakes, mainly during the first minutes of rain that wash litter, oil, heavy metals and other pollutants from roads. There are different technologies for the treatment of storm water, from retention ponds to intensive settling units. Table 1 - Typical performance of a storm water retention pond Parameter Pollutant removal in a storm water pond [ % ] BOD COD TSS Hydrocarbons

6 Figure 5 - Road storm water treatment by a commercial intensive settling unit Vegetation strips / ribbons surrounding the lake Strips of vegetation surrounding a lake and the rivers entering the lake absorb nutrients and stop suspended solids, drastically reducing the loading of pollution to the lake. Figure 6 - Examples of artificial and natural vegetation strips Land management in the catchment basin Erosion of the catchment basin may fill a lake with solids and nutrients. Erosion is generally due to excessive deforestation and bad agriculture practices. Figure 7 - Catchment basin management air photo of a good example of what should NOT be done 6

7 Reduce pollution from lake sediments (internal loading) Sediments at the bottom of the lake release dissolved organic matter and nutrients to the water column. This internal loading is sometimes more negative than the external loading by sewage and diffuse drainage. Mechanical removal of sediments Removing the sediments from a lake is a difficult and expensive practice, and the disposal of the sediments removed from the lake may be as difficult and expensive as the removal itself. Luckily, it is sometimes possible to use these sediments to construct artificial islands or gain coastal areas, and the real-state value of these new lands may cover the cost of sediment removal. Admir Environment is an Israeli firm that developed its own technology to dredge and dewater sediments from lakes and rivers. Figure 8 - Admir Environment technology for dredging and dewatering sediments 7

8 Bioaugmentation for the biological degradation of the sediments There are natural processes in the bottom of any lake that help to remove pollutants and improve lake situation. For example, anaerobic degradation of organic matter, denitrification, settling and immobilization of pathogen bacteria and parasites, etc. Bioaugmentation (the introduction of selected bacteria and enzymes to the lake) accelerates these natural processes and speeds lake restoration. Figure 9 - A two-year balance (in Tons) of Carbon, Nitrogen and Phosphorus in a wastewater reservoir in Israel Trapping P and other pollutants by coagulation Phosphorus is the main limiting factor for algae blooms in polluted lakes. The removal of P helps to maintain a proper oxygen balance and community development in lakes. Coagulants have been used to precipitate P and trapping it into the sediments; inactivated P is not released again to the water column. The technology is expensive and requires a correct application, but in some cases it is the best solution for the given situation of a lake. Alum is the most commonly used coagulant for this purpose, but other metals salts are also effective and today numerous commercial firms offer products which are a combination of several coagulants, some of them very effective. Coagulation also settles particles, resulting in short-term reduction of water turbidity. 8

9 Avoid resuspension of sediments by wind Wind produces waves and currents in lakes. Waves and currents may resuspend sediments and nutrients to the water column increasing the negative effects of pollution. The construction of artificial islands, barriers against long-shore currents and other coastal engineering structures reduce these negative effects. Figure 10 - Dirty wind-induced long-shore and rip currents in a reservoir in Israel 9

10 Removal of nutrients from lake water Periodic removal of weeds / water hyacinth from the lake is one of the practices for the removal of nutrients. But there are other alternatives. Floating constructed wetlands Floating islands properly constructed act as constructed wetlands, a proven technology for water treatment. Their use is still limited mainly to small lakes, but they may have an important effect in nutrient control, especially in nitrification / denitrification. Floating constructed wetlands can be designed and constructed following generic engineering procedures, but there are also several commercial firms offering specific technologies. Figure 11 - Floating constructed wetlands by Aquanea - Spain Figure 12 - Floating constructed wetlands by FloatingIslandsInternational - USA 10

11 In-lake nitrification/denitrification The Israel large experience with eutrophic and hypertrophic reservoirs indicates that, when nitrification occurs, denitrification runs fast in polluted water bodies. The limiting factor for nitrification / denitrification in water impoundments is the nitrification step. The addition of artificial substrata favors nitrification because nitrifying bacteria live better in attached growth. As quoted above, artificial islands may be one of these substrata but they are not the single alternative. Harvesting of weeds and water hyacinth Weeds and water hyacinth may overgrow in polluted lakes till become an unbearable nuisance. The periodic partial removal of this biomass has two direct benefits: returns areas of the lake to their original use: swimming, navigation, fishing, water source, etc. removes from the lake the nutrients contained in the biomass In some cases this biomass can be used a food for livestock or as feedstock for the production of biogas and fertilizers in anaerobic digesters. Figure 13 - Weeds in a polluted lake and one of the machines used to remove them 11

12 Figure 14 - Lake La Playa in Colombia fully covered by "buchón" (water hyacinth) Introduction of bugs that attack water hyacinths This technology may be VERY effective in removing water hyacinth. But its use is not always positive: If all water hyacinth is removed there is no nutrient uptake by water hyacinth and the nutrients become available to other photosynthetic organisms, situation that may lead to red tides = HABs- Hazardous Algal Blooms whose effect can be as negative as water hyacinths (or even more negative). Thus, the periodic mechanical removal of part of the water hyacinth (as quoted above) is sometimes more recommendable as a way to maintain an open lake while still removing nutrients from the ecosystem. 12

13 Biological control of algae and cyanobacteria blooms Overloading of nutrients results in uncontrolled growth of algae (algae blooms) and sometimes of cyanobacteria or other HABs-Hazardous Algal Blooms which may be toxic (very toxic!). Reduction of phosphorus in the water column is the most effective technology to avoid these blooms, but sometimes it must be complemented with alternative technologies that may help and even substitute nutrient reduction. Many red-tides or HABs are not due to a simple nutrient supply cause, but to a more complex relationship between nutrient supply and predation, as discussed by Theodore Smayda in his 2008 paper Complexity in the eutrophication harmful algal bloom relationship, with comment on the importance of grazing. Figure 15 - Cyanobacteria blooms in polluted lakes Figure 16 - NASA photo of toxic cyanobacteria bloom in warm mountain Lake Atitlán - Guatemala 13

14 Figure 17 - A HAB of toxic algae in a cold mountain lake Figure 18 - A "red-tide" of non-toxic photosynthetic purple bacteria in a hypertrophic reservoir in Israel 14

15 Sanitary fish for the biological control of plankton, weeds, organic sediments, etc. The introduction of sanitary fish allows the ecological manipulation of the biological community of the lake when it has been distorted by pollution. This technology was developed in Israel many years ago for the control of water quality in the reservoirs of the National Water Carrier (drinking water) and afterwards widely used for water quality control in aquaculture. Figure 19 - Some of the sanitary fish used in Israel Our colleague Dr. Ana Milstein from ARO-Israel has performed comprehensive research on fishenvironment-management, both in Israel and abroad, setting the scientific basis for this practice. Each situation requires the use of the different fish species in different proportions. Correct proportions lead to positive synergistic interactions, while wrong proportions result in unbalanced antagonistic interactions. 15

16 Figure 20 R&D on fish and water quality interactions in Bangladesh aquaculture ponds (Milstein et al.) The main species of sanitary fish used in Israel are: silver carp, Tilapia galilea --> phyto and zooplankton big-head carp --> zooplankton grass carp --> weeds black carp --> benthonic animals grey mullet, common carp --> organic matter in sediments sea bass --> fish Gambusia --> mosquitoes 16

17 Stratification rupture (de-stratification) and aeration of sediments Stratification divides the lake in two layers: warm epilimnion and cold hypolimnion, separated by a thermocline (a drastic temperature transition layer) sometimes a chemo-cline (salinity transition layer). In some cases the cline is thick enough to form a full layer, the metalimnion. Not all the lakes are stratified. The main factors determining stratification are: lake depth local climate conditions (altitude and altitude) lake size winds water turbidity Figure 21 - Schematic representation of stratification in a lake The hypolimnion may constitute a large portion of lake volume and it is anaerobic in polluted lakes, with very negative effects on water quality. A long experience indicates that the rupture of stratification (turnover) in polluted lakes allows the oxygenation of the whole water column and sediments, improving the quality of water and reducing the potential for toxic algae blooms. There are two basic technologies for destratification: 1. pumping surface oxygen-rich water to the bottom 2. pumping hypolimnion water to surface Different propellers, air-lifts and pumps can be used. Experience shows that the amount of energy required for lake destratification is generally small. Some warm mountain polluted lakes present an unusual situation: an anaerobic epilimnion above a well oxygenated hypolimnion, due to the entry of cold-cleanoxigenated water from surrouding mountains. Different types of devices are used for lake destratification, applicable to different situations and lake sizes. Figure 22 - Simple axial jet aerator used in Israel for destratification & aeration of wastewater storage reservoirs 17

18 Figure 23 - The SBP-Stratification Breaking Propeller device used for R&D in Israel by Dr. Ana Milstein Figure 24 - Lake mixer moved by solar energy (SolarBee USA) 18

19 Ultrasound The use of ultrasound devices has been proposed for the control of toxic cyanobacteria in polluted impoundments. The ultrasound breaks down the walls of algae, mainly the floating vacuole of toxic cyanobacteria such as Microcystis. The technology is relatively new and not fully proved, but positive results have been reported. There are several commercial firms selling this technology, some of them on solar energy. Figure 25 - Ultrasound for algae control by SonicSolutions USA and BIOTANK - Spain 19

20 Removal of garbage / litter / trash Trash is a serious type of pollution: it is visually unpleasant for swimming and tourism development, seriously affects fishing, adds toxic compounds endangering the drinking use of water, covers full areas of bottom lake killing the bottom biological community, etc. Urban lakes in public parks use to receive trash directly from public or by wind. Large lakes, on the contrary, receive most trash from the rivers feeding the lake or direct sewage discharges. Several technological alternatives are used to prevent the entry of trash into lakes and rivers, most of them based on different types of screens from very simple to most sophisticated. In small lakes it is possible to construct relatively simple devices for the automatic removal of floating trash. Figure 26 - Two examples of screens used to remove trash from large volumes of water 20

21 Construction of artificial islands and/or coastal land The construction of artificial islands and/or the filling of low coastal lands have numerous positive aspects. Some examples of artificial islands and their use can be found at Figure 27 - Mexcaltitan de Uribe México, ancient artificial island in lake allegedly birthplace of Aztec Empire For disposal of the sediments being removed from the lake The removal of polluted sediments from the bottom of the lake creates a serious problem: the disposal of these sediments. The in-site construction of artificial islands and/or filling of coastal areas generally is the lowest-cost disposal alternative. To reduce wind resuspension of sediments at downward coast Wind can resuspend sediments in the downward coast of the lake, reintroducing nutrients and turbidity to lake water. The construction of artificial islands to protect the coast from waves solves this problem when it exists. 21

22 To pay for the cost of lake restoration by selling new valuable land areas The land areas created by the disposal of removed sediment have a high real-state value as new land for residential areas and/or infrastructures such as marinas, tourism resorts, town parks, etc. The selling of these real-state lands may partially cover the costs of the expensive lake restoration. Figure 28 Wilhelmstein artifical island in Lake Steinhude - Germany constructed in XVIII Century To fill undesirable coastal swamps that may be a source of mosquitoes-malaria problems Some lakes have swamps in low level coastal lands, a source of mosquitoes which constitute a serious problem in malaria and dengue areas. The sediments removed from the bottom of the lake can be used to rise and dry these swamps. Figure 29 - A swamp in a low-level coastal area of a lake 22