UPGRADING WASTEWATER TREATMENT FACILITIES

Upgrading Wastewater Treatment Facilities



Upgrading Wastewater Treatment Facilities

Introduction

The aim of the present study is to investigate the fate of heavy metals in the Oranienburg sewage water plant before and after the use of chemical coagulants. Fate of metals in the precipitates and the produced sludge are also investigated. The level of metals in the sewage water as well as the sludge throughout every process of the plant (i.e. screening, grit chamber, primary sedimentation, sludge hydrolysis, aeration for nitrification, and secondary sedimentation) is also studied. In addition, a semi-technical scale for the anaerobic reactor of sludge is carried out in the plant. The purpose of this reactor is to produce a source of carbon to be available for the denitrification process (i.e. to improve the C/N ratio which is too low at present). This anaerobic digestion is carried out at an acidified pH-value around 6.0 - 6.5. Such decreases in pH would certainly increase the solubilities of certain metals in the sewage water. Therefore, the fate of heavy metals in the sludge before and after the anaerobic digestion is also an objective of the present study.

The arising questions are: What is the fate of heavy metals in the sludge before and after the anaerobic process? What is the level of these metals in the final wastewater effluent and the sludge? Can such produced sludge be used for agriculture purposes?

Materials and methods

The diagram of the sewage water treatment plant at Oranienburg is shown in Figure 1.

The technical data of the Oranienburg treatment plant are as follows:

Wastewater treatment capacity: at 40,000-50,000 PE; flowrate: at 5,500 m3/d.

Fine screen with a bar distance of 20cm.

Tangential grit chamber: with turbulent zones for mixing quicklime and FeCl3 wastewater at pH ~ 9.0.

Two primary sedimentation tanks: volume 2 ¥ 510m3 retention time: 3h.

Aeration tank: volume: 2,280m3; loading: at 0.15kg BOD5/kg MLSSxd; SVl: at 250/kg; sludge age: 10d.

Two secondary sedimentation tanks: volume: 2 ¥ 1,280m3; retention time: 3h.

Sludge treatment: two open tanks: volume: 2 ¥ 4,200m3; retention time: 60d.

Sludge polder: retention time: several months.

Sludge hydrolysis: volume: 80; retention time: 0.7-2d; pH around 6.0-6.5.

Dose of lime = 120 g/m3 (20 per cent); dose of FeCl3 = 8.4g Fe+3/m3[4glas FeCl3/m3] at 14

Weekly samples of the wastewater and/or sludge were collected for a period of 12 successive weeks. The wastewater samples were freshly filtered through Whatman No. 4 equivalent filter paper, acidified to below pH 2.0 using analytical reagent (AR) of nitric acid. The sludge samples were oven dried at 105°C for 24 hours. A known weight of each sludge sample was acid digested using AR nitric acid followed by AR hydrogen peroxide, according to US Environmental Protection Agency.

Metal concentrations in these wastewater and sludge samples were determined using Varian atomic absorption spectrometer, model SpectrAA-400 equipped with GA 1-96 graphite tube atomizer, attached by IBM personal computer AT (programmed for Varian-SpectrAA-300/400). The studied metals are Cr, Ni, Cd, Pb, Cu and Zn.

Discussion

The invention pertains to the treatment of wastewater to remove and/or biochemically modify carbonaceous and nitrogenous ...