RU2162059C1 - Method of removing heavy metals from waste waters from solid domestic waste dumps - Google Patents

Abstract

FIELD: waste water treatment. SUBSTANCE: method is realized by treating waste waters and recycling them through bulk of waste. For treatment, waste water is mixed with lime milk to pH 9.0-9.5. Treated waste water is then spread throughout the surface of dump with velocity 1-2 mm a day. Total amount of recycled treated waste water should not exceed 200-300 mm a year. Treatment is continued until achieving neutral reaction of waste water passed through drainage system. In case when filtrate has alkali reaction and concentration of heavy metals therein exceeds maximum permissible value, recycling of treated filtrate is continued to maximum reduction of heavy metal concentration. Process can be performed predominantly during warm period (spring, summer, autumn) at air temperature not below 0ю . Particularly important is using proposed method in yearly period of dump life. EFFECT: speeded up biological purification of waste water, increased degree of purification, and enabled process control. 2 cl

Description

 The invention relates to environmental protection, to utilities, and in particular to biological methods of wastewater treatment of solid domestic waste landfills and can be used mainly in a warm period of time (spring-summer-autumn) at an air temperature of not lower than 0 deg. FROM. Especially relevant is the use of the proposed method for landfills in the initial period of their operation.

 Biological methods of treating drainage wastewater of municipal solid waste (MSW) are known, for example, by repeatedly recirculating drainage wastewater through the mass of waste stored at the landfill (1). As a result of repeated recycling of solid waste water, they are cleaned of organic and inorganic contaminants (COD and BOD are reduced by 40-50%), heavy metal ions (cleaning effect is 50-60%), the pH of the medium increases, the transition of dangerous acid processes accelerates in the inner layers of waste flowing during the initial period of operation of the landfill, to the methane stage, the salinity of the waste increases, and the life cycle of the landfill is reduced.

 The reasons that impede the achievement of the required technical result are that the wastewater treatment process is very long (about 7 years), because recirculation is carried out by acidic wastewater, and their repeated return to the waste mass increases the decomposition of organic fractions and also leads to an increase in temperature in the surface layers of solid waste due to the activation of aerobic bacteria, which contributes to the ignition of the landfill. In addition, the cleaning effect of heavy metals is not high enough.

The closest set of essential features to the claimed method is a method of wastewater treatment by repeated recirculation, in which a neutralizing layer of calcium carbonate CaCO _{3 is} poured onto the waste surface before the recirculation process. In this case, neutralization of acidic wastewater occurs. The wastewater treatment process is carried out on average for 4 years (2).

 The reasons that prevent obtaining the required technical result are that when using this method, operational difficulties arise due to caking and cementing of the neutralizing layer, which lead to the formation of a waterproof layer on the surface of the landfill and the occurrence of random lateral leaks of acidic wastewater. The wastewater treatment process is quite long, and the degree of purification from heavy metals is low (up to 60%). In addition, when using this method, the process of managing wastewater treatment is difficult.

 The task to which the invention is directed is to reduce the time of biological wastewater treatment, the life cycle of a landfill, increase the degree of purification of acidic wastewater from heavy metals by neutralizing them, and also provide the ability to control the treatment process.

The problem is solved due to the fact that in the known method of wastewater treatment of solid domestic waste landfills from heavy metals by treating wastewater and recycling it, lime milk is used as a processing reagent - Ca (OH) ₂ solution. A solution of Ca (OH) _{2 is} actively mixed with wastewater (filtrate) to pH = 9.0-9.5 and distributed over the surface of the solid waste landfill at a rate of 1-2 mm per day, while the total amount of recycled filtrate in one section MSW should not exceed 200-300 mm / year.

The method is as follows. Wastewater is collected using a drainage system and discharged into special storage ponds. At the same time, a solution of the known milk Ca (OH) ₂ is prepared and the collected waste water is mixed in mixers with a solution of Ca (OH) ₂ for 10-15 minutes to a pH of 9.0-9.5. The necessary pH of the wastewater is created by changing the amount of Ca (OH) ₂ relative to the treated filtrate. The filtrate is treated with a solution of Ca (OH) ₂ at atmospheric pressure and natural air exchange. Next, the treated wastewater is distributed over the surface of the solid waste landfill at a rate of 1-2 mm per day, while the total amount of recycled filtrate in one section of solid waste should not exceed 200-300 mm / year. Otherwise, excess waterlogging will occur, which will lead to overflow of leachate and uncontrolled leakage of wastewater. In the case of separation of acidic filtrate, its processing before recirculation is carried out until the pH of the filtrate discharged by the drainage system is not lower than 7 (before the transition to the methane phase). In the case of separation of the filtrate with a pH of more than 7.0 (when the composition of the filtrate is in the methane phase), but containing high concentrations of heavy metals, the filtrate, pre-treated with a solution of milk of lime to pH = 9.0 - 9.5, is recycled to the maximum effect reduce the concentration of heavy metals in wastewater discharged by the drainage system.

где Me²⁺ - ион тяжелого метала, например, Fe²⁺, Mn²⁺, Zn²⁺ и т.д. Me(OH)₂ - нерастворимое соединение, выпадающее в осадок.In the process of liming, the main part of heavy metal ions will bind to insoluble hydroxides by the reaction:

where Me ²⁺ is a heavy metal ion, for example, Fe ²⁺ , Mn ²⁺ , Zn ²⁺ , etc. Me (OH) ₂ is an insoluble compound that precipitates.

Кроме этого, процесс обработки сточных вод известковым молоком будет способствовать обеззараживанию стоков от патогенной микрофлоры. Особенно это важно при обработке кислого фильтрата, значительно загрязненного патогенными энеторобактериями, яйцами гельминтов и жизнеспособными цистами кишечных простейших.The further supply of waste water treated with lime milk to the waste mass stored at the landfill accelerates the transition of the composition of effluent from the acid phase to the methane phase, while the redox potential will shift towards recovery processes. So sulfates will turn into sulfides by the reaction:
SO ₄ ^2- + 6H ⁺ = H ₂ S + 4OH
In this case, the concentration of heavy metals will decrease both due to the increased alkalinity of wastewater treated with milk of lime, and due to their binding to insoluble sulfides:

In addition, the process of treating wastewater with milk of lime will contribute to the disinfection of effluents from pathogenic microflora. This is especially important when treating acidic filtrate, significantly contaminated with pathogenic enetorobacteria, helminth eggs and viable intestinal protozoa cysts.

 An example of a specific implementation of the method.

 An experiment was conducted in a laboratory setting, during which a lot of crushed waste was subjected to repeated recycling of the resulting waste water treated with milk of lime. The composition of the investigated solid waste mass included paper waste 33%, food waste 20%, wood waste 15% mixed metal waste (iron, zinc, lead, etc.) 3%, the remaining waste was an inert material (glass, polyethylene , rubber, crushed stone, etc.). Preliminarily, the mass of solid waste was saturated with water to 80% moisture and biodegradable under optimal mesophilic conditions. The resulting acidic wastewater (pH = 4.5-5.0) was discharged from the bottom of the laboratory unit and mixed with a 1% solution of milk of lime for 10 minutes to pH = 9.0 -9.5. PH control was carried out using a laboratory pH meter. After that, the treated wastewater was distributed over the surface of the investigated waste at a rate of 2 mm per day. Additionally, water simulating precipitation in the amount of 2 mm per day was supplied to the surface of the waste. Recycling of the filtrate treated with lime milk was carried out until the concentration of heavy metals was reduced to the maximum permissible value for 6 months. It was found that preliminarily treating the recirculated filtrate with lime milk helps to reduce the concentrations of lead and iron in the final stock by 60 days. A significant decrease in zinc concentrations (by 98%) was observed on day 100 of the experiment. Repeated recycling of the pre-manufactured filtrate (to pH = 9.0–9.5) led to a significant decrease (by 70%) in the concentration of heavy metals in the drainage filtrate. The stabilization time of waste decomposition processes was halved.

Sources of information
1. An environmentally friendly landfill for the disposal of solid waste in Moscow. Environmental Protection Agency of Denmark. - M .: 1995. - 150 p.

 2. Christensen T., Cossu R. .. Stegmann R., Landfilling of Waste, Leachate, London and N.Y., 1992.

Claims (2)

1. The method of wastewater treatment of solid domestic waste landfills from heavy metals by treating wastewater and recycling it through the waste mass, characterized in that a solution of lime milk Ca (OH) ₂ , which is mixed with wastewater, is used as a reagent for treating wastewater up to pH 9.0 - 9.5, after which the treated wastewater is distributed over the surface of the solid waste landfill at a rate of 1 - 2 mm per day, with the total amount of wastewater recycled, pre-treated with lime milk municipal solid waste should not exceed 200 - 300 mm / year, processing is carried out until a neutral reaction medium wastewater discharged through the drainage system.  2. The method according to claim 1, characterized in that in the case of separation of the filtrate having an alkaline reaction of the medium, when the filtrate is in the methane phase, but with a concentration of heavy metals above the MAC, the recycle of the filtrate pre-treated with a solution of milk of lime to pH 9 , 0 - 9.5, carry out to the maximum effect of reducing the concentration of heavy metals in wastewater discharged by the drainage system.