Regional Solids Plant No. 5 Solids Handling Facility (RP-5 SHF)

Regional Plant No. 5 Solids Handling Facility (RP-5 SHF) is located on the southeast corner of the RP-5 facility site. It has been in operation since 2001.This facility is designed to process manure and food waste through an anaerobic digestion process. During this process, approximately 400,000 to 600,000 cubic feet/day of methane gas (bio-gas) is generated and used as a fuel source to operate engine generators that produce electricity. The electricity produced is used to operate equipment in the RP-5, RP-2 and Chino Desalter I facilities.

Plant Description
Unlike a typical wastewater treatment facility, the RP-5 SHF (Figure 1) does not receive wastewater from a collection system. This facility is designed to receive animal manure, primarily from dairy farms and food wastes from processing facilities within the Inland Empire valley. These materials are delivered to the RP-5 SHF by tanker trucks. The manure tanker trucks unload into a process that allows screening of large bulky material such as wood and rocks and from there, it is co-mixed with food wastes and pumped to anaerobic digesters. The food wastes are unloaded from the tanker trucks into storage tanks and subsequently co-mixed with the animal manure. Depending on the type of food wastes that is received, it is mixed in a given proportion with the animal manure to allow more uniform production of methane gas (bio-gas). Following the anaerobic digestion process, the solids or biosolids are dewatered by rotary presses and subsequently disposed of by land application and or made into compost at the Inland Empire Regional Composting Facility (IERCF). In addition, each treatment processes is integrated with instrumentation and control systems for controlling and monitoring various aspects of their operations. This overall facility instrumentation and control system is called the Supervisory Control and Data Acquisition (SCADA) System. The following subsections, briefly describe the functionality of each treatment area provided at RP-2.

Manure and Food Waste Biosolids Treatment
The animal manure and food wastes are co-mixed and pumped to three single stage anaerobic digester units. These treatment units reduce the volume of organic matter by decomposition of the biosolids into relatively stable organic and inorganic compounds from which water will separate more readily. In several ways, anaerobic digestion functions similarly to the human stomach when it digests food. Unlike the activated sludge process, the anaerobic digestion process is carried out in the absence of free oxygen by anaerobic microorganisms. wastewater biosolids are typically about 70 percent organic and about 30 percent inorganic or mineral. Much of the water in the biosolids is what is called “bound” water which will not readily separate from the biosolids. The anaerobic microorganisms’ breakdown the complex molecular structure of the biosolids which results in releasing the “Bound” water. During this release process, the microorganisms obtain oxygen from the water molecule and food from the remaining organic matter.

Unlike typical wastewater, the characteristics of animal manure and food wastes include high levels of proteins and lactose that are easily broken down by the anaerobic microorganisms. As a result, anaerobic decomposition of the manure and food waste will occur rapidly increasing the quantity and quality of byproducts such as carbon dioxide, hydrogen sulfide and methane gases.

At the RP-5 SHF, anaerobic digestion occurs by operating three single stage digester units in the mesophillic phase. This allows control on the time and temperature for digestion and stabilization of the biosolids and production of usable Methane Gas to fuel engine generators that produce electrical power.

Single stage mesophillic phase digestion; this method of anaerobic digestion is similar to the three phase anaerobic digestion process that is used at the Agencies RP-1 and RP-2 solids treatment processes except for it does not include the thermophillic or high temperature digestion phase. Because animal manure and food wastes contain higher amounts of proteins and sugars that can be easily broken down by the anaerobic microorganisms, decomposition of the organic matter occurs rapidly. Therefore, digestion or stabilization still occurs by the microorganisms attacking the biosolids soluble and dissolved organic matter such as the proteins and sugars. From these reactions, organic acids and gases such as carbon dioxide, hydrogen sulfide and low levels of methane are formed. This is known as the acid fermentation phase of anaerobic digestion and this process proceeds rapidly. Concurrent with this biological activity, this phase includes further decomposition, stabilization and gasification of the biosolids organic matter such as proteins and amino acids resulting in the production and predominance of relatively high quality methane gas. The methane gas is odorless, highly flammable and is used as a fuel source for operating engine generators to produce electrical power. The operating temperature for this phase of digestion is maintained typically between 98 and 101 degrees F and requires about 25 to 30 days retention in the digester tank to achieve a relatively stable biosolids with most of the “bound” water released to enhance dewaterability of the biosolids. Figure 2, typically illustrates the single phase digestion process at the RP-5 SHF.

Biosolids Dewatering
The relatively stablebiosolids are removedfrom the mesophillic digester units on arotating basis and transferred to the biosolids dewatering facilities. Currently, this facility includes mechanical equipment referred to rotary presses that are designed to remove water from the biosolids. The biosolids dewatering operation consists of two basic steps including conditioning andcompression.

Biosolids conditioning; the biosolids conditioning step is very important and involves the addition of polymers that will help to agglomerate the biosolids particles into flocs and thus provide the initial separation of the solids from the water. This step also conditions the biosolids to build a structure into the solids flocs so they can withstand increasing pressure and shearing action.

Biosolids Compression; after conditioning of the biosolids, it is pumped to the rotary presses where the water is forced to separate from the biosolids by means of friction and low pressure. The biosolids are pumped to the rotary press that contain a rectangular channel and is rotated between two revolving stainless steelchrome plated screens. With the friction (or drag) and low pressure condition, the biosolids are compressed and the water passes through the revolving screens, is collected and discharged from the rotary press. This water is called filtrate and it is disposed of by discharging into the Santa Ana River Industrial Waste pipeline that goes to a facility operated by the Los Angeles County Sanitation District. As the water continues to separate and the biosolids continue to travel through the press channel, it forms a dryer biosolids.

The dewatered biosolids characteristic after the compression step is similar to moist mud and is referred to as “Cake”. The cake can typically range from about 18 to 22 percent solids. This means if you had one ton (2000 pounds) of 18 percent biosolids and removed 100 percent of the remaining water, the dry weight of the biosolids would be 360 pounds. Therefore, the higher the cake percent solids, the less water it contains and more solids can be disposed of in the same volume of biosolids.

The dewatered biosolids is discharged from the rotary presses into a hopper. From the hopper, the biosolids are loaded into trailers and subsequently hauled away for disposal by land application and or hauled to the IECRF where it is made into compost.