An integrated treatment and reuse system of dairy wastewater - a case study in the state of Hawaii

Abstract

Milk parlor wastewater in a dairy operation in Hawaii was investigated for its potential treatment and reuse. Two earthen settling ponds were served as settling process and another 10 acres of wetland were planted with California grass to receive the effluent from settling ponds. It was found that the present treatment systems still remained many problems, such as odor, potential groundwater contamination and surface water pollution. The effluent could not meet the requirements for either disposal or reuse. Improving and integrating other cost effective biological treatment component(s) to the existing lagoons is required in order to meet discharge or reuse standards. Several biological treatment technologies were evaluated and investigated as the alternatives. In order to improve these existed problems, a 5-S approach (system existed, short HRT, small investment, simple operation and maintenance, system thinking) is developed. Among the 5-S, development of a higher SRT (Solids Retention Time) for the bioreactor is essential in order to integrate this unit into the other 4-S. A bioreactor, which is the modification of UASB (Upflow Anaerobic Sludge Blanket) reactor, was investigated. It was found that more than 70-75% of TCOD (Total Chemical Oxygen Demand) removal efficiency and biogas production of 1.5l/l/day with CH4 content of 70-75% could be achieved at 8-15g COD/l/day. The unique operation of the developed bio-nest reactor is able to achieve a higher COD removal efficiency with high organic loading rate with simple design and operation. This unique bioreactor is able to provide better sludge distribution and less dead zone compared to the conventional UASB. The process performance, design and operation criteria of this bioreactor were presented, discussed and compared with the existing anaerobic filter reactor and UASB reactor for the treatment of milk parlor wastewater. It was found that this bioreactor is able to operate in the temperature of 22± 2°C compared to others (35 °C with high COD removal efficiency and biogas production. Thus, it can be easily integrated into the existing lagoon system (popularly in the United States) or integrated to the aerobic/intermittent aerobic treatment unit for further removal of carbon and nitrogen in order to be able to dispose, discharge or reuse. Based on the laboratory results and field investigation, a treatment and reuse systems is proposed to improve one of the existing milk parlor wastewater management system.