The aim of this presentation is to show and share some experiences related to decentralized sanitation addressing segregation, reuse and improvement of treated wastewater’s quality.

Wastewater Management Technologies

Introduction

• 2.5 billion people live without good sanitation;• 80% of users of improved sanitation live in rural areas;• In Sub-Saharan Africa, treating diarrhoea consumes 12% of the health budget;• Conventional system are neither an ecological nor an economical solution for sanitation problems.• To supply rural areas with adequate sanitation facilities, sustainable solutions modeled on decentralised systems are required.

SUMMARY

Decentralised Technologies on Wastewater Management Septic Tanks, Constructed Wetlands, Composting Toilets,

Biodigestor, Anaerobic Filter, Duckweed Lagoons Demonstration projects on Wastewater

Management Tanzania, India, Egypt, Brazil

Decentralised Sanitation Systems

• Collection, treatment, and final disposition of the wastewater on/or close to the location;

• Useful in treating wastes from residences, households, small villages, isolated communities, etc.

Advantages for decentralized systems: Economy of structural arrangements such as transportation,

reservation and elevation; Possibility for reuse of the effluent and potentiality for aquifer

recharging; A problem in a unit doesn’t collapse the whole system; Development of the local potentialities: small systems can be

designed, built and managed by local professional, improving the local economy.

Ecological Sanitation (EcoSan)

• Ecological Sanitation is a decentrilised sanitation system that understands human excreta, organic wastes and wastewater as a resource (not as a waste) with high potential for reuse and recycling.

• EcoSan systems enable a complete recovery of nutrients in household wastewater and their reuse in agriculture. They also help preserve soil fertility and safeguard long-term food security. Moreover, they minimise the consumption and pollution of water resources.

Ecological Sanitation (EcoSan) Stages (or Phases)

Waste segregation and possible utilization options. (UNESCO/IHP & GTZ, 2006)

Septic Tank

• The aim of primary treatment is to separate out heavy constituents (suspended solids) and particularly light constituents (floating solids and scum) from the sewage.

• Due to its low treatment efficiency in terms of nutrient removal, a secondary treatment is recommended to polish the final effluent.

• This system consists of a closed, often prefabricated tank and is usually applied for primary sewage treatment. The treatment consists of sedimentation, flotation and digestion procedures.

• Septic tank is designed to receive all kinds of domestic wastes (kitchen, domiciliar laundries, washrooms, latrines, bathrooms, showers, etc) and it is economically viable to attend to 100 inhabitants.

Constructed Wetland• Constructed Wetlands are man-made systems which aims to simulate

the treatment processes in natural wetlands by cultivating emergent plants e.g. reeds (Phragmites), bulrushes (Scirpus), and cattails (Typha) on sand, gravel, or soil media.

• Constructed wetlands can serve the same small communities as natural wetlands and can be incorporated into the treatment systems for larger communities as well;

• They are subdivided, basically, into two wide groups:

(i) Surface Flow (the water or sewage flows through the soil surface); and

(ii) Subsurface Flow. (Vertical and Horizontal Flow)

Subsurface Flow Constructed Systems

These systems are applied for treatment of wastewater with low SS content and COD < 500 mg/L. They are therefore an excellent technology for secondary treatment.

We can subdivide this group in two different types as following:

Subsurface Vertical Flow Constructed Wetland (VSFW)

Subsurface Horizontal Flow Constructed Wetland (HSFW)

Subsurface Vertical Flow Constructed Wetland (SVFW)

• In SVFW the wastewater is loaded onto the planted filter bed’s surface. The pollutants are removed or transformed by microorganisms that are attached to the filtersand and the plants’ root system.

• Due to the biofilm presents in the filter material, and high Oxygen concentration in the system, vertical flow systems have been applied for both BOD5 and SS removal and nitrification promotion;

• However, it is important ensure that the filter is not saturated or covered with water in order to secure a high oxygen level in the filter.

Subsurface Horizontal Flow Constructed Wetland (SHFW)

• In SHFW the sewage is uniformly fed in the inlet work and due to a longitudinal slight slope (~1%) the liquid flows through the pores of the filter bed until it reaches the outlet work.

• SHFW usually provide high treatment effect in terms of removal of organics (BOD5, COD) and suspended solids (SS). The removal of nitrogen and phosphorus is lower but comparable with conventional treatment technologies which do not include special nutrient removal step.

Composting Toilets• A composting toilet system contains and processes excrement, toilet

paper, carbon additive, and sometimes, food waste. • As a nonwater-carriage system, a composting toilet relies on

unsaturated conditions where aerobic bacteria break down waste.

• When exposed to an unfavorable environment for an extended period of time, most pathogenic microorganisms will not survive. However, caution is essential when using the compost end-product and liquid residual in case some pathogens survive.

• The composting unit must be constructed to separate the solid fraction from the liquid fraction and produce a stable, humus material with less than 200 MPN per gram of fecal coliform.

• If sized and maintained properly, a composting toilet breaks down waste 10 to 30% of its original volume.

Biogas Digestor• Biogas latrines and communal biogas plants are, in principle, a more

advanced form of the septic tank system. • When human excreta is combined with animal and agricultural

wastes and water, it will give off gas as it decomposes. • The mix of gases produced is called ‘biogas’ which can be used for

cooking and lighting.

• Biogas plants typically store the wastes for about 30 days which can remove some of the pathogenic organisms but by no means all.

Anaerobic Filter• Anaerobic filters are used for wastewater with a low content of

suspended solids (e.g. after primary treatment in septic tanks) and narrow COD/BOD ratio. Biogas utilisation may be considered in case of BOD > 1.000 mg/l.

• The anaerobic filter, also known as fixed bed or fixed film reactor, includes the treatment of non-settleable and dissolved solids by bringing them in close contact with a surplus of active bacterial mass.

• The larger the surface for bacterial growth, the quicker is the digestion.

Duckweed-Based Wastewater Stabilizations Ponds

• In general, duckweed ponds are used to treat domestic or agricultural wastewaters.

• Lemnaceae have the greatest capacity in absorbing macro-elements (e.g. nitrogen, phosphorus, potassium, calcium, sodium and magnesium among others);

• Effluents with both a high BOD and nutrient load may require adequate primary treatment to reduce the organic load.

• Plants must be harvested regularly in order to prevent dead plants forming bottom sludge.

TypeKind of treatment Kind of wastewater

treatedAdvantages Disadvantages Nutrients removal

Septic Tank sedimentation, flotation and digestion

Domestic wastewater (communities until 100 inhabitants)

Simple, durable, easy maintenance, small area required

Low treatment efficiency, necessity of a secondary treatment, effluent not odorless

COD, BOD, TSS; grease.

Subsurface Flow Constructed Wetlands

biological and physical processes

Domestic and agricultural wastewaters; small communities; tertiary treatment for industries.

Low or no energy requirements; Provide aesthetic, commercial and habitat value.

system clogging; recommended as a secondary treatment, large areas required;

TSS; COD; TN; TP.

Composting Toilets unsaturated and aerobic conditions provide biological and physical decomposition

human excreta, toilet paper, carbon additive, food waste

Resulting "humus" used as a resource; conservation of water resources; recycling of nutrients.

If not well sized and maintained can be a environmental problem and a threat for human being, due to its contaminant potential

Volume reduced from 10 to 30%; pathogens.

Biogas Digestor Sedimentation, flotation and digestion

human excreta, animal and agricultural wastes

Recycling of resource; gas produced is used for cooking and lighting

Biogas plants can be expensive to build and difficult to operate. Poor maintenance leads to loss of gas production and blockage of the digester tank with solids.

Similar to septic tanks systems; The long period of storage can also remove some pathogens.

Anaerobic Filter anaerobicdegradation ofsuspended anddissolvedsolids

pre-settleddomestic andindustrialwastewater ofnarrowCOD/BOD ratio

simple and fairly durable if well constructed and wastewater has been properly pre-treated, hightreatment efficiency, little permanent space required

costly in construction because of special filter material, blockage of filterpossible, effluent smells slightly despite high treatment efficiency

BOD, TDS, TSS

Duckweed Based Wastewater Stabilizations Ponds

sedimentation, anaerobic degradation and sludge stabilization

Domestic and agricultural wastewater;

No clogging risk; High nutrient removal rates

Necessity of large areas; necessity of constant harvesting; unsuitable in very windy regions.

BOD, SS, TN, TP, metals

Some best-practices in wastewater management are shown in the following picture. Different techniques on wastewater treatment and management of GEF and non-GEF projects are presented below.

Wastewater Demo Projects

Before the introduction of a Constructed Wetland system, the College was treating its wastewater through a combination of a mechanical aeration system and a pond. However, operation of the mechanical system failed because of high costs of electricity and lack of regular maintenance.

Kleruu Teacher’s College - Tanzania

The pond was malfunctioning, ignored, lacked de-slugging and released untreated effluent to the downstream communities.

Wastewater Demo Projects

A Subsurface Horizontal Flow Constructed Wetland was installed to replace the pond. The need to operate the mechanical system accordingly ceased.

The performance of the installed constructed wetland is very promising, with a BOD removal rate of 90%, 76% in nitrate and 69% in heavy metals (cupper and chromium).

Wastewater Demo Projects

Kleruu Teacher’s College - Tanzania

Lake Manzala Engineered Wetland Project (LMEWP)

Problem Analysis:

• A large number of towns and villages have no proper sanitary waste system. The most common solution adopted is septic tanks dug into the ground, some without proper flooring

• Agricultural drainage discharges flow untreated from farmers’ fields into the Nile river and then into the Mediterranean Sea. Most agricultural fields in Egypt are treated with chemical fertilizers, pesticides and face increasing salinity.

• Pollution of Lake Manzala has seriously threatened the health of local people and the viability of economic activities such as fisheries, raising livestock, and farming.

Wastewater Demo Projects

At Lake Manzala the wastewater is pumped into ponds where sediments are allowed to settle. The water then flows through 60 acres of constructed wetlands where more than 75 percent of toxins are removed. Even in its experimental stage, the wetland treated 25,000m3 of wastewater per day from the Bahr el-Baqar drain.

At just ¼ of the cost of conventional methods, the pilot wetland has removed 61 percent of the BOD, 80 percent of SS, 15 percent of TP, 51 percent TP, and 99 percent of total coliform bacteria.

Lake Manzala Engineered Wetland Project (LMEWP)

Wastewater Demo Projects

Decentralized Wastewater Management at Adarsh College - India

This School Project is a Pilot Project demonstrating alternative decentralized sanitation solutions to the Badlapur Municipality Council. The Council plans to replicate the concept in other areas after evaluating the findings of decentralized reuse-oriented school sanitation project.The number of students attending Senior and Junior College is about 1,400 and 1,200 per day, respectively.

Applied sanitation components

Wastewater Demo Projects

Decentralized Wastewater Management at Adarsh College - India

Anaerobic Baffled Reator Anaerobic Filter

Vertical flow constructed wetlands - New Danish Guidelines

In order to achieve the requirements of Danish Ministry of Environment for single houses and dwellings in rural areas, a full-scale system was constructed to treat the sewage from a single household with four persons.The sewage was pre-treated in a three-chamber sedimentation tank (septic tank) prior to discharge into the vertical flow wetland to minimise the risk of clogging of pipes and the vertical filter.

Wastewater Demo Projects

It can be seen from the Table above that recirculation of water results in lower effluent concentrations, and hence better performance. The inlet concentration also decreases, but this is artificial because of the dilution from the recirculated effluent water to the sedimentation tank.

Due to its low performance in phosphorus removal, the system might be extended with a simple chemical dosing system in the sedimentation tank to remove this nutrient.

Wastewater Demo ProjectsVertical flow constructed wetlands -

New Danish guidelines

Duckweed Lagoons - ZimbabweThis Study was carried out to investigate the potential use of Duckweed -Based Waste Stabilization Ponds for wastewater treatment in small urban areas in Zimbabwe.The final effluent from Gutu Growth Point is discharged into nearby gum plantation before flowing into nearby river.

• The system have performed well in relation to nitrogen uptake;

• Despite the high phosphate levels in the effluent, the reduction rate is a sign that Duckweed Lagoon is an alternative for phosphorus removal in wastewater treatment.

• The total duckweed cover in the maturations ponds suppressed the growth of algae that normally results in a build up of Total Suspended Solids when the algae die.

Removal BOD 50%COD 50%Nitrates 70%Phosphates 80%TSS 90%

Wastewater Demo Projects

• Santa Catarina has 7.2 millions swine

• Each swine produce 10L swine waste/d

= 26 millions m3/year = 650.000t COD/year= 35.000t N/year= 15.000t P/year

Many researchers believe that swineculture is an activity with the biggest responsibility for water resources environmental impact.

Biogas Demo Projects

Swineculture and Water - Brazil

CH4

CO2

Electricity generator by Biogas

Food Methane Combustion= CO2

Swine waste

Duckweeds Lagoon