ANAEROBIC METHODS OF WASTE WATER TREATMENT

SANT LONGOWAL INSTITUTE OF ENGINEERING AND TECHNOLOGYDEPERTMENT OF FOOD TECHNOLOGY

LONGOWAL,SANGRUR,148106 Submitted to - Submitted by –

Dr. Parmjit S. Panesar (FET) Vishal Nag(gft/14/1310)

(Deptt of Biotechnology)

INTRODUCTION

Anaerobic treatment, being a biological treatment, many similarities to aerobic treatment. Until recently biological

treatment has meant an aerobic process in which oxygen is supplied by aeration to allow aerobic bacteria to break down and

assimilate the wastes. The supply of air is a major operational expense of this process. Large quantities of sludge are also

produced, which may or may not have resale value. If no resale opportunity exists, sludge disposal is another major expense

associated with the process.

Anaerobic process system diagram

Various Types Of Process Involved In Systems

In the (Down flow stationary fixed film) DSFF reactor systems, virtually all of the active biomass is attached to the support media. Different types of support media such as needle punched polyester (NPP) and red drain tile clay, PVC or glass can be used. For NPP, this attachment is probably associated with its surface roughness. The leaching of minerals from the clay could potentially stimulate bacterial activity and adhesion to this media support. Selection of proper inoculum source is important to obtain rapid reactor start-up and minimize the time required for the initial biofilm establishment. Usually a bacterial flora adapted to the target wastewater should be used. In general, the volume of inoculum used should at least 10% (v/v) to obtained good result.

Expanded Bed Process

In the expanded bed process, the wastewater to be treated is pumped upward through a bed of appropriate medium on which a biological growth has been developed. Effluent is recycled to dilute the incoming wastewater and to provide an adequate flow to maintain the bed in an expanded condition. Biomass concentrations exceeding 15,000 to 40,000 mg/L can be developed. Since more biomass can be maintained, the expanded bed process can also be used for the treatment of low strength wastewater, such as municipal sewage, at very short hydraulic retention times. Organic loading in the range of 5 to 10 kg COD / m3 can be applied with COD removal efficiency of 80 to 85 %. The hydraulic retention time generally will be in the range of 5 to 10 hours.

Anaerobic Contact Process

The essential feature of the anaerobic contact process is that the washout of the active anaerobic bacterial mass from the reactor is controlled by a sludge separation and recycles system. The major problem in the practical application of the contact process has always been the separation (and concentration) of the sludge from the effluent solution. For this purpose several methods have been used or were recommended for use, e.g. plain sedimentation, settling combined with chemical flocculation, with vacuum degasification, floatation and centrifugation. A basic idea underlying the contact process is that it is considered necessary to thoroughly mix the digester contents

Process flow charts

Wastewater treatment

Stages of treatment

STage1 primary treatment Stage 2 secondary treatment Stage 3 Tertiary treatment Stage 4 Sludge treatment

Different types of primary treatment

Process ApplicationScreening Removal of coarse suspended solidGrift Removal Removal of gritty materialFat traps Removal of free oil & greaseFlow Balancing To check function in hydraulic & pollutant loading

Anaerobic process

Generally for high bod con. >2500 mg/l or for high flow, low strength waste water

Suspended & attached growth process. Highly sensitive to shock loads or change in process parameters Low nutrient removal Energy recovery possible offering payback Low operating cost

PSYCHROPHILIC ANAEROBIC TREATMENT PROCESS

Although anaerobic wastewater treatment plants for municipal wastewater have been successfully operated in tropical countries such as Mexico, Columbia, India and China, the process until now has not been applied in countries with moderate and low temperatures. At such temperatures, chemical oxygen demand (COD) removal is limited and long hydraulic retention time is needed for one step system to provide sufficient hydrolysis of particulate organics. Low temperature causes deleterious effect on anaerobic digestion because of relatively longer generation time of anaerobic bacterial populations and lower biochemical activity, resulting in the decrease of biogas yield and digester failure. The start-up and treatment of municipal wastewater in cold regions was investigated in two UASB reactors operated at temperatures of 32, 20, 15, 11, and 6° C with several HRTs ranging from 48 to 3 h.

Biomass aggregation (granulation) was achieved in approximately 281 d at 20°C. However, low temperature or psychrophilic (< 20٥C) anaerobic digestion has recently been

proven feasible for the treatment of range of industrial wastewater representing a technological breakthrough for environmental management.

Therefore psychrophilic anaerobic treatment is an attractive option to conventional anaerobic digestion for wastewaters that are discharged at moderate to low temperature.

Application of UASB Reactor for Wastewater Treatment Waste water

Characteristics Granulation of biomass is indicative of successful operation of UASB reactor. Although, acceptable efficiency from the reactor can be obtained when sludge is in flocculent form, existence of granulation sludge configuration offers distinct advantages. The composition of wastewater plays an important role in granulation process. Substrates that support granulation are carbohydrates or proteins mainly in soluble, and possibly in colloidal form. Industrial wastewaters from sugar industry, breweries, apple juice, yeast factory, and grape wine satisfy this criterion and give granulation in UASB reactor.

Effects of low temperature on the physical and chemical properties of

wastewater Factors Affecting Of Anaerobic Digestion pH, Acidity and Alkalinity Temperature Nutrients Inhibitory Substances :- 1. Volatile Acids Inhibition 2. Ammonia Nitrogen Inhibition 3. Sulphide Inhibition 4. Heavy Metals Inhibition

Anaerobic Wastewater Treatment Microbiology

Anaerobic treatment of organic matter ‐ Anaerobic digestion 1. In the absence of O2, organic matter is fermented to

carbon dioxide and methane: 2CH2O ‐‐‐‐‐‐‐‐> CH4 + CO2

2. More than 75% of treatment plants in the US use anaerobic digestion to reduce the sludge yields, also energy produced. Sludge [though less of it] is still produced. Some facilities burn the sludge (costly), while other haul it away, e.g. landfill cover, off‐shore dump site, land application of 'bio solids'.

3. Also used directly for treatment of municipal wastewater, mostly in Europe, and for agriculture/farm wastes. In addition, in Europe, used for high organic industrial wastes (e.g. canning/food wastes).

Merits of Anaerobic Decomposition Process

  1. A high degree of waste stabilization; 2. A low production of excess biological sludge and this sludge can be directly dried and

rying bed without further treatment due to better dewatering ability; 3. Low nutrient requirements, hence anaerobic treatment is attractive for the treatment of wastewater where external nutrient addition is required; 4. No oxygen requirement, hence saving in power required for supply of oxygen in aerobic

methods; 5. Production of valuable by product, methane gas; 6. Organic loading on the system is not limited to oxygen supply hence higher loading rate

as compared to aerobic processes can be applied. 7. Less land required as compared to many aerobic process. 8. Non-feed conditions for few months do not affect adversely to the system and this makes

it attractive option for seasonal industrial wastewater treatment.

Demerits of Anaerobic Decomposition Process

1. Lower treatment efficiencies (about 5-10% less than in activated sludge processes if no post-treatment is installed.

2. H2S content in the gas can lead to problems with bad smell and corrosion.

3. No nutrients (N, P) are removed without post treatment. 4. Compared to pond systems, a rather poor pathogen removal if no

post treatment is installed. 5. Compared to pond systems, a high demand for operational know-

how. 6. Economically not feasible for sewage temperatures below at 15*c. 

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