Ex. 13. Scan the following text and speak on every stage of sewage (wastewater) treatment. Then render the text in Russian.

TEXT C. SEWAGE (WASTEWATER) TREATMENT PROCESS (continuation)

Primary treatment consists in temporarily holding the sewage in a quiescent basin called “primary clarifier” or “primary sedimentation/ settling tank”. The main purpose of primary treatment is the physical separation of solids and grease from the wastewater (heavy solids settle to the bottom while oil, grease and lighter solids float to the surface to be skimmed off). The settled and floating materials (sludge) are removed, separately treated or processed, and a homogeneous liquid is subjected to secondary (biological) treatment. As a result of primary treatment, 30-40% of Biological Oxygen Demand (BOD) and 50% of Total Suspended Solids are removed. Primary clarifiers are equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank from where it can be pumped to further sludge treatment stages.

Secondary treatment is designed to degrade the biological content of the sewage (dissolved and suspended biological matter derived from human waste, food waste, soaps and detergent) using aerobic biological processes. The purpose of biological treatment is BOD reduction. The principle of the process is that simple bacteria (cells) eat the organic matter which is transformed into cellular mass (floc) through their metabolism. The floc is precipitated at the bottom of a settling tank or retained as slime on solid surfaces. There are two broad types of biological treatment:

1. the treatment that includes mechanical means to create contact between wastewater, cells and oxygen:

· activated sludge (aerated sewage containing aerobic microorganisms that help to break it down); such aerobic biological wastewater treatment is accomplished in activated sludge tanks;

· trickling filters and rotating biological contactors where the biomass (biological films of bacteria, protozoa and fungi) grows on the media’s surface and eats or otherwise reduces the organic content.

2. the treatment without mechanical means:

· the sewage is made to flow by gravity through specially constructed lagoons or wetlands where vegetation acts as a biological filter to the water.

Tertiary treatment provides a final treatment stage to remove disease-causing organisms and to increase the effluent quality (of 10 parts per million BOD and 10 parts per million Total Suspended Solids) before it is discharged back into the environment. Tertiary treatment processes can be physical, biological, or chemical including:

· sand filtration (to remove residual suspended matter) or activated carbon filtration (to remove residual toxins);

· lagooning (to provide further biological improvement through storage in large artificial ponds or lagoons);

· nitrogen and phosphorus removal;

· disinfection (to reduce the number of microorganisms) using chlorine, ozone O₃, or ultraviolet (UV) light;

· odour removal.

More than one tertiary treatment process may be used at any treatment plant.

***activated sludge – активный [активированный] ил (масса, состоящая из органических веществ и микроорганизмов, образующаяся в аэрационном бассейне и ускоряющая процессы окисления и очистки сточных вод)

activated sludge tank – аэрационный бассейн

BOD (biochemical oxygen demand) – БПК, биохимическая потребность в кислороде

contactor – контактный фильтр

homogeneous [ˌ hɔ mə 'ʤ iː nɪ ə s] liquid – однородная жидкость

lagoon – лагуна; отстойный бассейн, отстойный пруд

lagooning – сброс и очистка сточных вод в прудах-отстойниках

mechanically driven – с механическим приводом

primary clarifier – первичный отстойник

quiescent [kwɪ 'es(ə)nt] – находящийся в покое, неподвижный

sand filtration – песчаная фильтрация

sedimentation/ settling tank – отстойный резервуар, отстойник

skim off – очищать поверхность; снимать (накипь и т.п.)

Total Suspended Solids – общее содержание взвешенных частиц; общее количество суспендированного, взвешенного в воде материала; нефильтруемый остаток

trickling filter – биофильтр; капельный фильтр